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