EXHIBIT 5.1
                                 LAW OFFICES OF

                          PILLSBURY MADISON & SUTRO LLP
LOS ANGELES                   POST OFFICE BOX 7880               MENLO PARK
NEW YORK                 SAN FRANCISCO, CALIFORNIA 94120         ORANGE COUNTY
SACRAMENTO                  TELEPHONE (415) 983-1000             SAN DIEGO
SAN FRANCISCO               TELECOPIER (415) 983-1200            SAN JOSE
WASHINGTON, D.C.                                                 HONG KONG
TOKYO





                                             January 23, 1997


Fair, Isaac and Company, Incorporated
120 North Redwood Drive
San Rafael, CA 94903


     Re:  Registration Statement on Form S-3


Ladies and Gentlemen:

     We are acting as counsel for Fair, Isaac and Company, Incorporated, a
Delaware corporation (the "Company"), in connection with the registration under
the Securities Act of 1933, as amended, of 21,000 shares of Common Stock, $0.01
par value (the "Common Stock"), of the Company, to be offered and sold by
certain stockholders of the Company (the "Selling Stockholders"). In this regard
we have participated in the preparation of a Registration Statement on Form S-3
relating to such 21,000 shares of Common Stock. (Such Registration Statement, as
amended, is herein referred to as the "Registration Statement.")

     We are of the opinion that the shares of Common Stock to be offered and
sold by the Selling Stockholders have been duly authorized and legally issued
and are fully paid and nonassessable.

     We hereby consent to the filing of this opinion as Exhibit 5.1 to the
Registration Statement and to the use of our name under the caption "Legal
Matters" in the Registration Statement and in the Prospectus included therein.

                                        Very truly yours,

                                        PILLSBURY MADISON & SUTRO LLP