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                                                                       EXHIBIT 5

                              M&T Bank Corporation
                                  One M&T Plaza
                                Buffalo, NY 14203



                                                         December 12, 2000

Board of Directors
M&T Bank Corporation
One M&T Plaza
Buffalo, NY  14203

Ladies and Gentlemen:

        This opinion is rendered in connection with the Registration Statement
on Form S-4, No.-333-48946 (the "Registration Statement"), of M&T Bank
Corporation, a ("M&T"), filed with the Securities and Exchange Commission under
the Securities Act of 1933, as amended (the "Securities Act"), relating to the
registration of 9,023,214 shares of M&T's common stock, par value $.50 per share
("M&T Common Stock"), isuable in connection with that certain Agreement and Plan
of Reorganization dated as of July 9, 2000 (the "Reorganization Agreement"),
among M&T, Premier National Bancorp, Inc. ("Premier"), and Olympia Financial
Corp. ("Olympia"), and that certain related Agreement and Plan of Merger dated
as of July 9, 2000, as amended(together, the "Agreements"), among M&T, Premier
and Olympia. Subject to certain conditions, the Agreements provide for the
merger (the "Merger") of Premier with and into Olympia.

        As Senior Vice President and General Counsel of M&T, I have participated
in the preparation of the Registration Statement, including the prospectus
included therein. I have acted as counsel to M&T with respect to the
authorization and issuance of the M&T Common Stock covered by the Registration
Statement. I have reviewed M&T's Restated Certificate of Incorporation and
Bylaws, each as amended to date, the



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Board of Directors
M&T Bank Corporation
December 12, 2000
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Registration Statement, the Agreements and the proceedings taken by M&T relating
to the Agreements and the Registration Statement, including the resolutions
adopted by M&T's Board of Directors with respect thereto. I also have examined
such corporate records, certificates and other documents that I have considered
necessary or appropriate for the purposes of this opinion.

        In making such examination and rendering the opinions set forth below, I
have assumed: (i) the genuineness and authenticity of all signatures (other than
my own) on original documents; (ii) the authenticity of all documents submitted
to me as originals; and (iii) the conformity to originals of all documents
submitted to me as copies and the authenticity of all originals of such
documents. In addition, I have assumed the due authorization and issuance of the
outstanding shares of common stock of Premier in accordance with applicable law.
I am admitted to practice law in the State of New York and do not purport to be
an expert on or to express any opinion on any laws other than the laws of the
State of New York and the federal laws of the United States of America. This
opinion speaks as of today's date and is limited to present statutes,
regulations and judicial interpretations. In rendering this opinion, I assume no
obligation to revise or supplement this opinion should the present laws be
changed by legislative or regulatory action, judicial decision or otherwise.

        Based upon the foregoing, I am of the opinion that the shares of M&T
Common Stock issuable in the Merger have been duly authorized and, when issued
to the stockholders of Premier pursuant to, and in accordance with, the terms of
the Agreements, will be validly issued, fully paid and nonassessable.


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Board of Directors
M&T Bank Corporation
December 12, 2000
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        This letter does not address any matters other than those expressly
addressed herein. This letter is given for your sole benefit and use. No one
else is entitled to rely hereupon.

        I hereby consent to the filing of this opinion as an exhibit to
Pre-Effective Amendment No. 1 to the Registration Statement and to the reference
to me under the caption "Legal Opinion" in the prospectus, which is part of the
Registration Statement. In giving such consent, I do not thereby admit that I am
in the category of persons whose consent is required under Section 7 of the
Securities Act.

                                                  Very truly yours,

                                                  /s/ Richard A. Lammert
                                                  -----------------------
                                                  Richard A. Lammert
                                                  Senior Vice President and
                                                  General Counsel