Exhibit 5.1 [LETTERHEAD OF LATHAM & WATKINS] January 22, 2002 File No. 022142-0006 Amgen Inc. One Amgen Center Drive Thousand Oaks, California 91320 Re: Amgen Inc. Nonqualified Deferred Compensation Plan --------------------------------------- Ladies and Gentlemen: In connection with the registration under the Securities Act of 1933, as amended (the "Act"), of $207,400,000 in deferred compensation obligations (the "Obligations") of Amgen Inc. (the "Company") issuable under the Amgen Nonqualified Deferred Compensation Plan (the "Plan") on a Registration Statement on Form S-8 filed with the Securities and Exchange Commission (the "Commission") on January 22, 2002 (the "Registration Statement"), you have requested our opinion with respect to the matters set forth below. In our capacity as your special counsel in connection with such registration, we are familiar with the proceedings taken and proposed to be taken by the Company in connection with the issuance of the Obligations. In addition, we have made such legal and factual examinations and inquiries, including an examination of originals or copies certified or otherwise identified to our satisfaction of such documents, corporate records and instruments, as we have deemed necessary or appropriate for purposes of this opinion. In our examination, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals, and the conformity to authentic original documents of all documents submitted to us as copies. We are opining herein as to the effect on the subject transaction only of the federal securities laws of the United States, the internal laws of the State of California and General Corporation Law of the State of Delaware, and we express no opinion with respect to the applicability thereto, or the effect thereon, of the laws of any other jurisdiction, or in the case of Delaware, any other laws, or as to any matters of municipal law or the laws of any local agencies within any state. Subject to the foregoing, it is our opinion that upon the issuance of the Obligations in the manner contemplated by the Registration Statement and in accordance with the terms of the Plan, such Obligations will be legally valid and binding obligations of the Company. LATHAM & WATKINS Amgen Inc. January 22, 2002 Page 2 Our opinion is subject to: (i) the effect of bankruptcy, insolvency, reorganization, moratorium or other similar laws now or hereafter in effect relating to or affecting the rights or remedies of creditors; (ii) the effect of general principles of equity, including without limitation concepts of materiality, reasonableness, good faith and fair dealing and the possible unavailability of specific performance or injunctive relief, regardless of whether enforcement is considered in a proceeding in equity or at law; and (iii) the effect of the laws of usury or other laws or equitable principles relating to or limiting the interest rate payable on indebtedness. This opinion is rendered only to you and is solely for your benefit in connection with the transactions covered hereby. This opinion may not be relied upon by you for any other purpose, or furnished to, quoted to, or relied upon by any other person, firm or corporation for any purpose, without our prior written consent. We consent to your filing this opinion as an exhibit to the Registration Statement. Very truly yours, /s/ Latham & Watkins