QUESTIONS AND ANSWERS ABOUT THE MERGER AND SPECIAL MEETING

The exercise price for options to purchase 78,025 shares of Bank common stock is greater than the estimated per share merger consideration. Therefore, the Bank does not believe these 78,025 options will be exercised. If none of these options are exercised, the exchange ratio, based on the assumptions discussed above, will be 0.0616 shares of Prosperity common stock for each share of Bank common stock, subject to adjustment.

The merger consideration is subject to adjustment based on the ten (10) trading day average closing price of the Prosperity common stock in the manner and under the circumstances set forth in the reorganization agreement. The merger consideration is also subject to decrease in the event the Bank’s equity capital on the closing date of the merger is less than $16,750,000 in the manner and under the circumstances set forth in the reorganization agreement.

The holders of at least a majority of the shares of Bank stock entitled to vote at the special meeting must be present, either in person or by proxy, to constitute a quorum at the special meeting. Approval of the reorganization agreement by Bank shareholders requires the affirmative vote of the holders of at least two-thirds of the shares of Bank stock outstanding on August 9, 2012, the record date. Approval of the non-binding proposal regarding certain merger-related executive compensation arrangements requires the affirmative vote of the holders of a majority of the shares of Bank stock outstanding on the record date and present or represented at the meeting.

SUMMARY

This brief summary highlights selected information from this proxy statement/prospectus and may not contain all of the information that is important to you. We urge you to carefully read this entire document and the other documents we refer to in this document. These documents will give you a more complete description of the transaction we are proposing. For more information about Prosperity, see “Where You Can Find More Information” on page 82. We have included page references in this summary to direct you to other places in this proxy statement/prospectus where you can find a more complete description of the topics we have summarized.

The Companies

Prosperity Bancshares, Inc.

Prosperity Bank Plaza

4295 San Felipe

Houston, Texas 77027

(713) 693-9300

Prosperity, a Texas corporation, is a financial holding company pursuant to the Gramm-Leach-Bliley Act (the “GLB Act”) and bank holding company registered under the Bank Holding Company Act of 1956, as amended (the “BHC Act”). Through Prosperity Bank, its wholly owned subsidiary bank, Prosperity conducts a complete range of commercial and personal banking activities. Prosperity currently operates a total of two hundred thirteen (213) full service banking locations; fifty-nine (59) in the Houston area; twenty (20) in the South Texas area including Corpus Christi and Victoria; thirty-five (35) in the Dallas/Fort Worth area; twenty-one (21) in the East Texas area; thirty-four (34) in the Central Texas area including Austin and San Antonio; thirty-four (34) in the West Texas area including Lubbock, Midland/Odessa and Abilene; and ten (10) in the Bryan/College Station area. As of March 31, 2012, on a consolidated basis, Prosperity had total assets of $10.9 billion, total loans of $3.9 billion, total deposits of $8.5 billion and shareholders’ equity of $1.6 billion.

Community National Bank

5123 Bellaire Boulevard

Bellaire, Texas 77401

(713) 664-4777

Community National Bank is a national banking association which operates from one banking office located in Bellaire, Texas. The Bank was chartered in 2002. As of March 31, 2012, the Bank had total assets of $182.8 million, total loans of $68.7 million, total deposits of $162.6 million and shareholders’ equity of $17.4 million.

Proposed Merger of the Bank into Prosperity Bank

We have attached the reorganization agreement to this document as Appendix A. Please read the entire reorganization agreement. It is the legal document that governs the merger.

We propose a merger whereby the Bank will merge with and into Prosperity Bank. Prosperity Bank will be the surviving entity in the merger. Immediately following completion of the merger, the existing office of the Bank will become a full-service banking center of Prosperity Bank. We expect to complete the merger during the fourth quarter of 2012, although delays could occur.

Terms of the Merger of the Bank into Prosperity Bank (page 37)

Pursuant to the terms of the reorganization agreement, all outstanding shares of Bank stock will be converted into an aggregate of 372,396 shares of Prosperity common stock and $11,440,000 in cash, subject to

adjustment. More specifically, if the average closing price of the Prosperity common stock for the ten (10) consecutive trading days ending on and including the fifth trading day prior to the closing date of the merger, which we refer to herein as the average closing price, exceeds $52.16, the exchange ratio and/or the per share cash consideration will be decreased such that the aggregate value of the Prosperity common stock and cash equal no more than $30,864,175, as further described in this proxy statement/prospectus and the reorganization agreement.

In addition, if (1) the average closing price of the Prosperity common stock is less than $40.00 and (2) the Prosperity common stock underperforms the KBW Regional Banking Index by more than thirteen percent (13%) during the twenty (20) consecutive trading days ending on and including the fifth trading day prior to the closing date of the merger, Prosperity may increase the exchange ratio and/or the per share cash consideration such that the aggregate value of the shares of Prosperity common stock and cash equal at least $26,335,840, as further described in this proxy statement/prospectus and the reorganization agreement. The merger consideration is also subject to decrease in the event that the Bank’s equity capital on the closing date of the merger is less than $16,750,000, in the manner and under the circumstances set forth in the reorganization agreement.

The market price of Prosperity common stock will fluctuate from the date of this proxy statement/ prospectus to the date of completion of the merger, and these fluctuations could result in an adjustment of the exchange ratio and/or the per share cash consideration. Because of the possibility of an adjustment of the exchange ratio and/or the per share cash consideration, you will not know the exact number of shares of Prosperity common stock or the exact amount of cash you will receive in connection with the merger when you vote on the reorganization agreement.

Material U.S. Federal Income Tax Consequences (page 59)

The merger is intended to qualify as a reorganization under the Internal Revenue Code of 1986, as amended, or the Code. As a result of receiving a combination of common stock and cash in exchange for Bank stock, in general, shareholders of the Bank will recognize gain, but not loss, equal to the lesser of cash received or gain realized in the merger. The amount of gain realized will equal the amount by which the cash, if any, plus the fair market value, at the effective time of the merger, of the Prosperity common stock exceeds the basis in the Bank stock to be surrendered in exchange therefor.

This tax treatment may not apply to every shareholder of the Bank. Determining the actual tax consequences of the merger to you may be complicated and will depend on your specific situation and on variables not within our control. You should consult your own tax advisor for a full understanding of the merger’s tax consequences to you.

Opinion of the Bank’s Financial Advisor (page 41)

Commerce Street Capital, LLC has delivered a written opinion to the board of directors of the Bank that, as of the date of the reorganization agreement, based upon and subject to certain matters stated in the opinion, the merger consideration is fair to the holders of Bank stock from a financial point of view. We have attached this opinion to this document as Appendix B. The opinion of Commerce Street is not a recommendation to any Bank shareholder as to how to vote on the proposal to approve the reorganization agreement. You should read this opinion completely to understand the procedures followed, matters considered and limitations on the reviews undertaken by Commerce Street in providing its opinion.

Prosperity Plans to Continue to Pay Quarterly Dividends (page 77)

Following the merger, subject to applicable statutory and regulatory restrictions, Prosperity intends to continue its practice of paying quarterly cash dividends. For the second quarter of 2012, Prosperity paid a cash dividend of $0.195 per share.

Ownership of Prosperity After the Merger

Pursuant to the reorganization agreement and assuming no adjustment, Prosperity will issue approximately 372,396 shares of its common stock to Bank shareholders in connection with the merger. Based on this assumption, and 56,050,410 shares of Prosperity common stock outstanding as of August 6, 2012, after the completion of the merger, the former Bank shareholders would own approximately 0.66% of the outstanding shares of Prosperity common stock.

Market Prices of Prosperity Common Stock (page 21)

Shares of Prosperity common stock are quoted on the New York Stock Exchange under the symbol “PB.” On June 26, 2012, the last trading day before the merger was announced, Prosperity common stock closed at $40.33 per share. On August 6, 2012, Prosperity common stock closed at $40.02 per share. The market price of Prosperity common stock will fluctuate prior to the merger. You should obtain the current stock quotation for Prosperity common stock. Shares of the Bank are not traded on any established public trading market. The most recent trade of the Bank’s common stock of which the Bank’s management is aware occurred on April 27, 2012, when 3,000 shares were traded at a price of $2.75 per share.

The Bank Special Shareholders’ Meeting (page 35)

The special meeting of shareholders of the Bank will be held on September 12, 2012, at 3:30 p.m., local time, at the main office of the Bank located at 5123 Bellaire Boulevard, Bellaire Texas 77401. At the special meeting, you will be asked:

Record Date Set at August 9, 2012; Votes Required (page 35)

You may vote at the special meeting of Bank shareholders if you owned Bank stock at the close of business on August 9, 2012. You can cast one vote for each share of Bank stock you owned at that time. As of August 6, 2012, there were 5,906,159 shares of Bank stock issued and outstanding.

Approval of the reorganization agreement requires the affirmative vote of the holders of at least two-thirds of the outstanding shares of Bank stock. Approval of the non-binding proposal regarding certain merger-related executive compensation arrangements requires the affirmative vote of the holders of a majority of the shares of Bank stock entitled to vote and present or represented at the meeting. If you fail to vote, it will have the effect of a vote against the reorganization agreement.

You may vote your shares of Bank stock by attending the special meeting and voting in person or by completing and mailing the enclosed proxy card. If you are the record holder of your shares, you can revoke your proxy at any time before the vote is taken at the special meeting by sending a written notice revoking the proxy or a later-dated proxy to the secretary of the Bank, or by voting in person at the special meeting.

The Bank’s Reasons for the Merger and Recommendations of the Bank’s Board of Directors (page 39)

Based on the reasons discussed elsewhere in this document, the board of directors of the Bank believes that the merger is fair to you and in your best interests, and unanimously recommends that you vote FOR the proposal to approve the reorganization agreement. For a discussion of the circumstances surrounding the merger and the factors considered by the Bank’s board of directors in approving the reorganization agreement, see page 39.

Members of the Bank’s Management are Expected to Vote Their Shares For Approval of the Reorganization Agreement

As of June 30, 2012, the directors and executive officers of the Bank (10 persons) were entitled to vote 1,223,281 shares of Bank stock, or approximately 20.7% of the outstanding shares of the common stock entitled to vote at the special meeting. Each of these directors and executive officers has executed an agreement to vote his or her shares of Bank stock in favor of approval of the reorganization agreement.

Effective Time of the Merger (page 48)

The merger will become effective at the date and time specified in the articles of merger to be issued by the Texas Department of Banking. If the Bank shareholders approve the reorganization agreement at the special meeting, and if all necessary government approvals are obtained and the other conditions to the parties’ obligations to effect the merger are met or waived by the party entitled to do so, we anticipate that the merger will be completed in the fourth quarter of 2012, although delays could occur.

We cannot assure you that the necessary shareholder and governmental approvals will be obtained or that the other conditions to completion of the merger can or will be satisfied.

Treatment of Outstanding Options (page 48)

Not later than ten (10) days after the Bank special meeting, the board of directors of the Bank intends to accelerate the exercise date for all outstanding options to acquire Bank stock for a limited period of time to expire on a date chosen by the Bank board of directors. On or before such specified date, each Bank option may be exercised for cash by the holder of such option. After such date, all unexercised options will terminate. If all outstanding options are exercised by the holders thereof, the Bank would be obligated to issue 194,625 shares of Bank stock prior to the merger. The exchange ratio set forth in this proxy statement/prospectus assumes the issuance of such shares. The exercise price for options to purchase 78,025 shares of Bank common stock is greater than the estimated per share merger consideration. Therefore, the Bank does not believe these 78,025 options will be exercised.

Exchange of Bank Stock Certificates (page 47)

As soon as practicable after the effective time of the merger, you will receive a letter and instructions from Computershare Investor Services, acting in its role as Prosperity’s transfer and exchange agent, with respect to the procedures for surrendering your stock certificates representing shares of Bank stock in exchange for stock certificates representing shares of Prosperity common stock and cash. You must carefully review and complete these materials and return them as instructed along with your stock certificates for the Bank stock. Please do not send the Bank or Prosperity any stock certificates until you receive these instructions.

Conditions to Completion of the Merger (page 51)

The completion of the merger depends on a number of conditions being met. These include, among others:

Additionally, the completion of the merger depends on the execution of the following agreements, all of which have been executed, but will not become effective until the effective time of the merger:

Any condition to the consummation of the merger may be waived in writing by the party to the reorganization agreement entitled to the benefit of such condition. A party to the reorganization agreement could choose to complete the merger even though a condition has not been satisfied, as long as permitted by law. We cannot be certain when or if the conditions to the merger will be satisfied or waived, or that the merger will be completed.

Regulatory Approvals Required (page 63)

We cannot complete the merger unless it is approved by the Federal Deposit Insurance Corporation (FDIC) and Texas Department of Banking (TDB). We expect to obtain all necessary regulatory approvals, although we cannot be certain if or when we will obtain them. On July 9, 2012, Prosperity filed an application with the FDIC and TDB to obtain approval of the merger. The U.S. Department of Justice will have between 15 and 30 days following approval by the FDIC to challenge the approval on antitrust grounds. While the Bank and Prosperity do not know of any reason that the Department of Justice would challenge regulatory approval by the FDIC and believe that the likelihood of such action is remote, there can be no assurance that the Department of Justice will not initiate such a proceeding, or if such a proceeding is initiated, as to the result of any such challenge.

Modifications or Waiver (page 57)

We may amend the reorganization agreement and each of us may waive our right to require the other party to adhere to any term or condition of the reorganization agreement. However, the merger consideration to be received by the shareholders of the Bank pursuant to the reorganization agreement may not be decreased after the approval of the reorganization agreement without further approval by Bank shareholders.

Termination of the Reorganization Agreement (page 57)

Prosperity, Prosperity Bank and the Bank can mutually agree at any time to terminate the reorganization agreement without completing the merger. In addition, either Prosperity or the Bank can decide, without the consent of the other, to terminate the reorganization agreement if:

The Bank may terminate the reorganization agreement, without the consent of Prosperity, if:

In addition, Prosperity may terminate the reorganization agreement, without the consent of the Bank, if:

Prosperity also has the right to terminate the reorganization agreement on or prior to September 25, 2012 if the results of any environmental inspections or surveys of the Bank properties identify certain potential or current violations of environmental laws or environmental law requires certain remedial or clean up action that could have a material adverse effect on the Bank.

In the event of the termination of the reorganization agreement without breach by any party, the reorganization agreement will be void and have no effect, without liability on the part of any party or the directors, officers or shareholders of any party, except as specifically contemplated in the reorganization agreement or as set forth below.

Termination Fee (page 58)

If the reorganization agreement is terminated by:

then the Bank will be required to pay Prosperity a termination fee of $1,500,000.

If either Prosperity or the Bank terminates the reorganization agreement after December 24, 2012 (or February 22, 2013, if regulatory approval has not been obtained by December 24, 2012) and the Bank’s shareholders have not approved the reorganization agreement by such date, or, without regard to timing, if the Bank’s shareholders do not approve the reorganization agreement and an acquisition proposal exists at the time of termination, the Bank will be required to pay Prosperity up to $250,000 for its expenses related to the proposed transaction.

If Prosperity or the Bank terminates the reorganization agreement because the Bank’s shareholders fail to approve the reorganization agreement and, within twelve (12) months of termination of the reorganization agreement, the Bank enters into an acquisition agreement with a third party, the Bank will be required to pay Prosperity a termination fee of $1,500,000, in addition to the $250,000 for its expenses related to the proposed transaction previously paid.

Some of the Directors and Officers of the Bank Have Financial Interests in the Merger that Differ from Your Interests (page 55)

Some of the directors and officers of the Bank have interests in the merger that differ from, or are in addition to, their interests as shareholders of the Bank. These interests include the following:

Comparison of Rights of Shareholders of Prosperity and the Bank (page 65)

The Bank is a national banking association and the rights of shareholders of the Bank are governed by the laws of the United States and the Bank’s articles of association and bylaws. Prosperity is a Texas corporation and the rights of Prosperity shareholders are governed by Texas law and Prosperity’s articles of incorporation and bylaws. Upon completion of the merger, shareholders of the Bank will become shareholders of Prosperity and their rights will be governed by Prosperity’s articles of incorporation and bylaws in addition to Texas law. Prosperity’s articles of incorporation and bylaws will remain the same unless later altered, amended or repealed.

Dissenters’ Rights of Appraisal in the Merger (page 64)

As a shareholder of the Bank, under the National Bank Act you have the right to dissent from the merger and have the appraised fair value of your shares of Bank common stock paid to you in cash. The appraised fair value may be more or less than the value of the shares of Prosperity common stock and cash being paid in the merger. Persons having beneficial interests in Bank common stock held of record in the name of another person, such as a broker or bank, must act promptly to cause the record holder to take the actions required under the National Bank Act to exercise your dissenter’s rights. The text of 12 U.S.C. Section 214a pertaining to dissenters’ rights is attached to this proxy statement/prospectus as Appendix C.

In order to exercise dissenters’ rights, you must (1) not vote in favor of the reorganization agreement or give notice of dissent to the Bank at or prior to the special meeting and (2) give the written notice required by the National Bank Act to Prosperity following the special meeting.

If you intend to exercise dissenters’ rights, you should read the statute carefully and consult with your own legal counsel. You should also remember that, if you return a signed proxy card but fail to provide instructions as to how your shares of Bank common stock are to be voted, you will be considered to have voted in favor for the reorganization agreement and you will not be able to assert dissenters’ rights. Also, if you exercise dissenters’ rights, you may have taxable income as a result, so you should consult with your own tax advisor if you intend to dissent. See “—Income Tax Consequences.”

Recent Developments

Preliminary Financial Results of Prosperity for the Six Months Ended June 30, 2012

On July 27, 2012, Prosperity announced unaudited preliminary results for the six months ended June 30, 2012. Net income for the period was $73.5 million or $1.55 per diluted common share compared with $69.0 million or $1.47 per diluted common share for the same period in 2011, an increase of $4.5 million or 6.5%. For the six months ended June 30, 2012, Prosperity’s return on average assets was 1.37% and its return on average common equity was 9.10%. For the same period, Prosperity’s net interest income before the provision for loan losses was $165.5 million compared with $164.0 million during the same period in 2011, an increase of 0.9%. The increase was attributable primarily to a 13.0% increase in average earning assets over the same period. Prosperity’s net interest margin on a tax-equivalent basis was 3.60% for the six months ended June 30, 2012, compared with 4.04% for the same period in 2011.

At June 30, 2012, Prosperity had total assets of $10.74 billion, total loans of $3.95 billion, total deposits of $8.39 billion and total shareholders’ equity of $1.64 billion.

Prosperity’s nonperforming assets totaled $11.9 million or 0.13% of average earning assets at June 30, 2012 compared with $12.7 million or 0.15% of average earning assets at June 30, 2011. The allowance for loan losses was $50.4 million, or 1.28% of total loans, at June 30, 2012 compared with $51.9 million, or 1.42% of total loans, at June 30, 2011.

The following table presents Prosperity’s selected consolidated financial data as of and for the six months ended June 30, 2012 and 2011. The financial data set forth below is unaudited and should be read in conjunction with Prosperity’s consolidated financial statements and notes to the consolidated financial statements contained in reports that Prosperity has previously filed with the Securities and Exchange Commission. See “Where You Can Find More Information” on page 82. You should not assume that the results of operations for past periods and any interim period indicate results for any future period.

Preliminary Financial Results of the Bank for the Six Months Ended June 30, 2012

The net loss of the Bank for the six months ended June 30, 2012 was $39,000 or $0.01 per basic and diluted common share compared with net earnings of $406,000 or $0.07 per basic and diluted common share for the same period in 2011, a decrease in net income of $445,000 or 1,141.03%. The decrease was primarily due to the decrease in net interest income and a $700,000 provision for possible credit losses, which was partially offset by a reduction in noninterest expense. For the six months ended June 30, 2012, the Bank’s return on average assets was (0.004)% and its return on average equity was (0.44)%. For the six months ended June 30, 2012, the Bank’s net interest income before the provision for possible credit losses was $2.7 million compared with $3.4 million for the same period in 2011, a decrease of 21.4%. The decrease was attributable primarily to the reduction in loan volume from the sale of the Pearland branch in 2011 along with the reinvestment of funds from loan reductions and cash flow derived from the mortgage-backed securities portfolio into lower interest rate investments. The Bank’s net interest margin was 3.09% for the six months ended June 30, 2012, compared with 3.82% for the same period in 2011.

As of June 30, 2012, the Bank had total assets of $180.6 million, total loans of $68.6 million, total deposits of $162.6 million and total shareholders’ equity of $17.8 million.

The Bank’s nonperforming assets totaled $1.7 million or 0.94% of total assets at June 30, 2012 compared with $3.1 million or 1.72% of total assets at June 30, 2011. The allowance for possible credit losses was $1.0 million, or 1.50% of total loans, at June 30, 2012 compared with $1.2 million, or 1.36% of total loans at June 30, 2011.

The following table presents the Bank’s unaudited selected financial data as of and for the six months ended June 30, 2012 and 2011. You should not assume that the results of operations for past periods and any interim period indicate results for any future period.

Selected Historical Consolidated Financial Data of Prosperity

The following table summarizes financial results actually achieved by Prosperity for the periods and as of the dates indicated and should be read in conjunction with Prosperity’s consolidated financial statements and the notes to the consolidated financial statements contained in reports that Prosperity has previously filed with the Securities and Exchange Commission. Historical financial information for Prosperity can be found in its Quarterly Report on Form 10-Q for the quarter ended March 31, 2012 and its Annual Report on Form 10-K for the year ended December 31, 2011. See “Where You Can Find More Information” on page 82 for instructions on how to obtain the information that has been incorporated by reference. Financial amounts as of and for the three months ended March 31, 2012 and 2011 are derived from Prosperity’s unaudited interim consolidated financial statements, which Prosperity’s management believes reflect all adjustments (consisting only of normal recurring adjustments) necessary for a fair presentation of its results of operations and financial position as of the dates and for the periods indicated. You should not assume the results of operations for past periods and for any interim period indicate results for any future period.