EXHIBIT 8.1

                                Andrews & Kurth
                      Mayor, Day, Caldwell & Keeton L.L.P.
                             600 Travis, Suite 4200
                              Houston, Texas 77002

                                January 9, 2002

Riverway Holdings, Inc.
Five Riverway
Houston, Texas 77056

                                  TAX OPINION

Ladies and Gentlemen:

    We have acted as counsel for Riverway Holdings, Inc. ("Riverway"), a Texas
corporation, in connection with the merger (the "Merger") of Riverway with and
into Texas Regional Delaware, Inc. ("Texas Regional Delaware"), a Delaware
corporation and wholly owned subsidiary of Texas Regional Bancshares, Inc.
("Texas Regional"), a Texas corporation, pursuant to the Agreement and Plan of
Reorganization, dated as of September 17, 2001, by and between Riverway, Texas
Regional and Texas Regional Delaware, as amended (the "Merger Agreement").

    At your request, in connection with the filing of the Registration Statement
on Form S-4 with the Securities and Exchange Commission on the date hereof (the
"Registration Statement"), we are rendering our opinion concerning certain
federal income tax consequences of the Merger. In connection with rendering our
opinion, we have reviewed the Merger Agreement, the Registration Statement, the
proxy statement/prospectus which is contained in and made part of the
Registration Statement (the "Proxy Statement"), certificates of officers of
Texas Regional, Texas Regional Delaware and Riverway as to factual matters and
such other documents and corporate records as we have deemed necessary or
appropriate as a basis therefor.

    We have assumed that the representations and warranties contained in the
Merger Agreement were true, correct and complete when made and will continue to
be true, correct and complete through the effective time of the Merger, and that
the parties have complied with and, if applicable, will continue to comply with
the covenants contained in the Merger Agreement. We also have assumed that
statements as to factual matters contained in the Registration Statement and the
Proxy Statement are true, correct and complete, and will continue to be true,
correct and complete through the effective time of the Merger. Finally, we have
assumed that the representations and covenants to be executed by Texas Regional,
Texas Regional Delaware and Riverway pursuant to Section 6.8 of the Merger
Agreement will be true, correct and complete through the effective time of the
Merger and that such covenants will be complied with in all material respects.

    Subject to the limitations and qualifications set forth herein, the opinions
attributable to us in the discussion under the caption "Material United States
Federal Income Tax Consequences of the Merger" in the Proxy Statement included
in the Registration Statement filed in respect of the transactions contemplated
in the Merger Agreement are our opinion with respect to the matters set forth
therein.

    Our opinions are based upon our interpretations of current United States
federal income tax law, including court authority and existing Final and
Temporary Regulations, which are subject to change both prospectively and
retroactively, and upon the facts and assumptions discussed herein. This opinion

                              Exhibit 8.1--Page 1

letter is limited to the matters set forth herein, and no opinions are intended
to be implied or may be inferred beyond those expressly stated herein. Our
opinion is rendered as of the date hereof and we assume no obligation to update
or supplement this opinion or any matter related to this opinion to reflect any
change of fact, circumstances, or law after the date hereof. In addition, our
opinion is based on the assumption that the matter will be properly presented to
the applicable court. Furthermore, our opinion is not binding on the Internal
Revenue Service or a court. In addition, we must note that our opinion
represents merely our best legal judgment on the matters presented and that
others may disagree with our conclusion. There can be no assurance that the
Internal Revenue Service will not take a contrary position or that a court would
agree with our opinion if litigated.

    We hereby consent to the references to our firm and this opinion contained
in the Proxy Statement included in the Registration Statement and to the filing
of this opinion as an exhibit to the Registration Statement. Subject to the
continued truthfulness, correctness and completeness of the representations and
warranties described in this opinion, we will confirm this opinion on the
effective date of the Merger.

                                          Very truly yours,
                                          /s/ Andrews & Kurth
                                          Mayor, Day, Caldwell & Keeton L.L.P.

                              Exhibit 8.1--Page 2