Exhibit 5.1


                                  May 17, 2002

Warren Bancorp, Inc.
10 Main Street
Peabody, MA 01960

Ladies and Gentlemen:

This opinion is furnished in connection with the registration, pursuant to the
Securities Act of 1933, as amended (the "Securities Act"), of 360,000 shares
(the "Shares") of common stock, par value $.10 per share ("Common Stock"), of
Warren Bancorp, Inc., a Massachusetts corporation (the "Company"), pursuant to
the Company's 2002 Stock Option and Incentive Plan (the "Plan"). This opinion is
being furnished in accordance with the requirements of Item 601(b)(5) of
Regulation S-K under the Securities Act.

         In connection with rendering this opinion, we have examined the
Articles of Organization and the Bylaws of the Company, each as amended; such
records of the corporate proceedings of the Company as we deemed material; a
registration statement on Form S-8 under the Securities Act relating to the
Shares (the "Registration Statement"), the Plan, and such other certificates,
receipts, records and documents as we considered necessary for the purposes of
this opinion.

         In our examination, we have assumed the legal capacity of all natural
persons, the genuineness of all signatures, the authenticity of all documents
submitted to us as originals, the conformity to original documents of all
documents submitted to us as certified, conformed or photostatic copies and the
authenticity of the originals of such latter documents. In making our
examination of documents executed or to be executed, we have assumed that the
parties thereto, other than the Company, had or will have the power, corporate
or other, to enter into and perform all obligations thereunder and have also
assumed the due authorization by all requisite action, corporate or other, and
execution and delivery by such parties of such documents and the validity and
binding effect thereof on such parties. As to any facts material to the opinions
expressed herein that we have not independently established or verified, we have
relied upon oral or written statements and representations of officers and other
representatives of the Company and others. We have assumed that the certificates
representing the Shares will be signed by an authorized officer of the transfer
agent and registrar for the Common Stock and registered by such transfer agent
and registrar and will conform to the specimen thereof examined by us. We have
also assumed that each award agreement setting forth the terms of each grant of
options or other awards under the Plan will be consistent with the Plan and will
be duly authorized and validly executed and delivered by the parties thereto,
and that that no options or other awards will be granted under the Plan with
exercise or purchase prices below the par value of the Shares, no adjustment to
the exercise price of any option or purchase price of any award will result in a
reduction of the price per Share issuable thereunder to a price below the par
value of the Shares at the time of exercise or purchase and that the
consideration received by the Company for each of the Shares delivered pursuant
to the Plan will be in an amount at least equal to the par value thereof.

         We are attorneys admitted to practice in the Commonwealth of
Massachusetts. We express no opinion concerning the laws of any jurisdictions
other than the laws of the United States of America and the Commonwealth of
Massachusetts.

         Based upon and subject to the foregoing, we are of the opinion that the
Shares have been duly authorized for issuance by the Company, and, when such
Shares are issued, delivered and paid for upon



exercise of options or stock purchase rights duly granted under the terms and
conditions of the Plan, such Shares will be validly issued, fully paid and
nonassessable.

         The foregoing assumes that all requisite steps will be taken to comply
with the requirements of the Securities Act and applicable requirements of state
laws regulating the offer and sale of securities.

         We hereby consent to the filing of this opinion with the Commission as
Exhibit 5 to the Registration Statement. In giving this consent, we do not
thereby admit that we are included in the category of persons whose consent is
required under Section 7 of the Securities Act or the rules and regulations of
the Securities and Exchange Commission.


                                             Very truly yours,

                                             /s/ GOODWIN PROCTER LLP

                                             GOODWIN PROCTER LLP