EXHIBIT 5.1

                          [MCGUIREWOODS LLP LETTERHEAD]

                                January 30, 2004

SPSS Inc.
233 South Wacker Drive
Chicago, Illinois 60606

RE: REGISTRATION STATEMENT ON FORM S-3

Ladies and Gentlemen:

         We refer to the Registration Statement on Form S-3 (the "Registration
Statement") being filed by SPSS Inc., a Delaware corporation, (the "Company")
with the Securities and Exchange Commission under the Securities Act of 1933, as
amended (the "Securities Act"), relating to the issuance and sale of up to
281,830 shares of Common Stock, $0.01 par value per share (the "Common Stock")
of the Company in connection with that certain Stock Purchase Agreement, dated
as of November 4, 2003, by and among the Company, SPSS International, B.V. and
the former shareholders of Data Distilleries B.V.

         Each term used herein that is defined in the Registration Statement and
not otherwise defined herein shall have the meaning specified in the
Registration Statement.

         We are familiar with the proceedings to date with respect to the
proposed offering of the Common Stock and have examined such records, documents
and questions of law, and satisfied ourselves as to such matters of procedure,
law and fact, as we have considered relevant and necessary as a basis for the
opinion expressed in this letter. In such examination, we have assumed the
genuineness of all signatures, the authenticity of all documents submitted to us
as originals, the conformity to originals of all documents submitted to us as
certified copies or photocopies and the authenticity of the originals of such
documents.

         Based on the foregoing, and subject to the qualifications set forth
hereinafter, we are of the opinion that the Common Stock has been duly
authorized and, when issued and sold in accordance with the Registration
Statement, will be legally issued, fully paid and nonassessable shares of Common
Stock of the Company.

         This opinion is limited to the matters set forth herein. No opinion may
be inferred or implied beyond the matters expressly contained herein.

         We hereby consent to the reference to our firm under the caption "Legal
Matters" in the Registration Statement and the related Prospectus, and to the
filing of this opinion as an Exhibit to the Registration Statement.

                                                     Very truly yours,

                                                     /s/ McGuireWoods LLP