UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON D.C. 20549 FORM 11-K (Mark One) [X] ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year end December 31, 1999 OR [_] TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number 000-12477 AMGEN RETIREMENT AND SAVINGS PLAN (Full title of the plan) AMGEN INC. (Name of issuer of the securities held) One Amgen Center Drive, Thousand Oaks, California 91320-1799 (Address of principal executive offices) (Zip Code)

Amgen Retirement and Savings Plan Financial Statements and Supplemental Schedule Years ended December 31, 1999 and 1998 Contents Report of Independent Auditors.......................................... 1 Audited Financial Statements Statements of Net Assets Available for Benefits......................... 2 Statements of Changes in Net Assets Available for Benefits.............. 3 Notes to Financial Statements........................................... 4 Supplemental Schedule Schedule Schedule of Assets Held for Investment Purposes at End of Year.......... A

Report of Independent Auditors Amgen Inc., as Named Fiduciary, and the Plan Participants of the Amgen Retirement and Savings Plan We have audited the accompanying statements of net assets available for benefits of Amgen Retirement and Savings Plan as of December 31, 1999 and 1998, and the related statements of changes in net assets available for benefits for the years then ended. These financial statements are the responsibility of the Plan's management. Our responsibility is to express an opinion on these financial statements based on our audits. We conducted our audits in accordance with auditing standards generally accepted in the United States. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion. In our opinion, the financial statements referred to above present fairly, in all material respects, the net assets available for benefits of the Plan at December 31, 1999 and 1998, and the changes in its net assets available for benefits for the years then ended, in conformity with accounting principles generally accepted in the United States. Our audits were performed for the purpose of forming an opinion on the financial statements taken as a whole. The accompanying supplemental schedule of assets held for investment purposes at end of year as of December 31, 1999, is presented for purpose of additional analysis and is not a required part of the financial statements but is supplementary information required by the Department of Labor's Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. The supplemental schedule is the responsibility of the Plan's management. The supplemental schedule has been subjected to the auditing procedures applied in our audits of the financial statements and, in our opinion, is fairly stated in all material respects in relation to the financial statements taken as a whole. /s/ Ernst & Young LLP May 26, 2000 Los Angeles, California 1

Amgen Retirement and Savings Plan Statements of Net Assets Available for Benefits December 31 1999 1998 -------------------------------- Assets Investments at fair value $694,704,196 $438,830,171 Employee contributions receivable 871,467 800,426 Employer contributions receivable 1,087,551 935,605 Accrued interest and dividends 24,232 38,096 -------------------------------- Net assets available for benefits $696,687,446 $440,604,298 ================================ See accompanying notes. 2

Amgen Retirement and Savings Plan Statements of Changes in Net Assets Available for Benefits Year ended December 31 1999 1998 --------------------------------- Additions to net assets: Employee contributions $ 34,456,717 $ 28,214,758 Employer contributions 25,751,763 22,813,735 Interest and dividend income 31,970,804 18,966,190 Realized/unrealized gain 178,969,323 90,894,285 --------------------------------- Total additions 271,148,607 160,888,968 Deductions from net assets - benefits paid (15,065,459) (15,091,254) --------------------------------- Net increase 256,083,148 145,797,714 Net assets available for benefits at beginning of year 440,604,298 294,806,584 --------------------------------- Net assets available for benefits at end of year $696,687,446 $440,604,298 ================================= See accompanying notes. 3

Amgen Retirement and Savings Plan Notes to Financial Statements December 31, 1999 1. Description of Plan The following description of the Amgen Retirement and Savings Plan (the Plan) provides only general information. Participants should refer to the Plan document for a more complete description of the Plan's provisions. General The Plan was established effective April 1, 1985 (amended and restated effective January 1, 1990, January 1, 1993 and April 1, 1996, respectively), as a defined contribution plan covering substantially all domestic employees of Amgen Inc. (the Company). It is subject to the provisions of the Employee Retirement Income Security Act of 1974 (ERISA). Contributions Participants may contribute up to 15% of their pretax annual compensation (a maximum contribution of $10,000 in 1999 and 1998). Participants may also contribute amounts representing distributions from other qualified defined benefit or defined contribution plans. The Company contributes 100% of the first 5% of eligible salary contributed by the employee per pay period. In addition, the Company supplements the above contribution for all eligible employees, whether or not they have elected to make contributions to the Plan, with a Core contribution equal to 3% of each eligible employee's compensation each pay period. Participants select the funds in which their contributions are to be invested, electing among various investment alternatives. Participants may elect for their contributions to be invested in more than one fund; however, no more than 50% of their total contributions may be invested in the Amgen Inc. Stock Fund. Participants may change their investment options at any time. Vesting Participants are immediately vested with respect to their individual contributions and earnings thereon. Participants become vested in their allocated Company matching contributions and related earnings on a pro rata basis over a four-year period once they 4

Amgen Retirement and Savings Plan Notes to Financial Statements (continued) 1. Description of Plan (continued) Vesting (continued) have worked in excess of 1,000 hours within a Plan year. The Company Core contributions become 100% vested after five years of service, with no partial vesting during the five-year period. Company contributions become fully vested upon attainment of normal retirement age, disability or death. Participant Accounts Each participant's account is credited with the participant's contributions and an allocation of (a) Company contributions and (b) Plan earnings. The benefit to which a participant is entitled is the benefit that can be provided from the participant's account. Forfeited balances of terminated participants' nonvested accounts are used to reduce future Company contributions. Payments of Benefits Upon retirement, a participant may elect to receive a lump-sum payment in cash and/or shares of the Company's common stock. The number of shares of Company common stock to be paid is based on the quoted market value of such stock on the date the Plan is valued following employee notification. Participants hired before April 1, 1996 may also elect to have an insurance annuity contract purchased on the participant's behalf. Certain restrictions apply to withdrawals of amounts from the Plan while a participant continues to be employed by the Company. Participant Loans Loans can be made to a participant generally up to the lesser of an amount equal to 50% of the participant's vested account balance or $50,000, less any outstanding loans. The loans bear interest at average borrowing rates of certain major banks (ranging from 9.43% to 11.87%) and are generally payable in installments over periods ranging from one to five years. Principal and interest payments are allocated to the participant's account. 5

Amgen Retirement and Savings Plan Notes to Financial Statements (continued) 1. Description of Plan (continued) Plan Termination Although it has not expressed any intent to do so, the Company has the right under the Plan to terminate the Plan subject to the provisions of ERISA. In the event of termination, participants will become 100% vested in their accounts. Trustee Fidelity Management Trust Company acts as the Plan's trustee. 2. Summary of Significant Accounting Policies Basis of Accounting The financial statements have been prepared on the accrual basis of accounting. Reclassification Certain amounts in the 1998 financial statements have been reclassified to conform to the 1999 presentation. Investment Income Dividend income is recognized on the ex-dividend date and interest income is recorded on an accrual basis. Unrealized gains and losses on investments are measured by the change in the difference between the fair value and cost of the securities held at the beginning and end of the period. Realized gains and losses from security transactions are recorded based on the weighted-average cost of securities sold. Investment Valuation Investments in mutual funds and Amgen Inc. common stock are valued at current market values determined through reference to public market information on the last business day of the Plan year. Participant loans are valued at their outstanding balances which approximate fair value. 6

Amgen Retirement and Savings Plan Notes to Financial Statements (continued) 2. Summary of Significant Accounting Policies (continued) Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. 3. Investments The fair value of individual investments that represent 5% or more of the Plan's net assets are as follows: December 31 1999 1998 ------------------------------ Amgen Inc. Stock Fund $231,234,930 $89,745,146 Fidelity Magellan Fund 113,828,967 83,941,345 Fidelity Growth and Income Portfolio 82,202,660 76,567,285 Fidelity Retirement Money Market Portfolio 31,237,779 22,169,268 Fidelity Overseas Fund 35,396,995 23,822,171 Fidelity Spartan U.S. Equity Index 52,567,255 42,385,329 Fidelity OTC Portfolio 57,066,911 27,810,796 During 1999 and 1998, the Plan's investments (including gains and losses on investments bought and sold, as well as held during the year) appreciated in value by $178,969,323 and $90,894,285, respectively, as follows: Year ended 1999 1998 -------------------------------- Amgen Inc. Stock Fund $127,089,607 $42,404,859 Mutual funds 51,879,716 48,489,426 -------------------------------- $178,969,323 $90,894,285 ================================ 7

Amgen Retirement and Savings Plan Notes to Financial Statements (continued) 4. Income Tax Status The Plan has received a determination letter from the Internal Revenue Service dated July 23, 1997, stating that the Plan is qualified, in form, under Section 401(a) of the Internal Revenue Code (the Code) and, therefore, the related trust is exempt from taxation. Once qualified, the Plan is required to operate in conformity with the Code to maintain its qualification. The Company believes the Plan is being operated in compliance with the applicable requirements of the Code and, therefore, believes that the Plan is qualified and the related trust is tax exempt. Subsequent amendments have been structured to, and are intended to, maintain the Plan's tax qualified status. 5. Services Provided by the Company The Company provides certain administrative and recordkeeping services for the Plan at no cost to the Plan participants. In addition, the Company has paid the trustee fees and other related costs on behalf of the Plan. 8

Supplemental Schedule

Schedule A Amgen Retirement and Savings Plan EIN: 95-3540776 Plan: 35274 Schedule H, line 4i - Schedule of Assets Held for Investment Purposes at End of Year December 31, 1999 Description of Current Identity of Issue Investment Cost Value - ----------------------------------------------------------------------------------------------------------------- Amgen Inc.* Common stock 3,808,081 shares $59,361,905 $231,234,930 Fidelity Magellan Fund* Mutual fund 833,118 shares 78,989,453 113,828,967 Fidelity Growth and Income Portfolio* Mutual fund 1,743,059 shares 57,729,842 82,202,660 Fidelity Retirement Money Market Portfolio* Money market portfolio 31,237,779 31,237,779 Fidelity Overseas Fund* Mutual fund 737,284 shares 24,949,317 35,396,995 Fidelity Spartan U.S. Equity Index* Mutual fund 1,009,162 shares 32,310,152 52,567,255 Fidelity Short-Term Bond* Mutual fund 1,026,942 shares 8,900,605 8,729,012 Fidelity OTC Portfolio* Mutual fund 839,590 shares 33,409,853 57,066,911 Fidelity Asset Manager* Mutual fund 692,669 shares 11,915,575 12,731,262 Fidelity Asset Manager: Growth* Mutual fund 1,035,241 shares 18,648,431 20,363,189 Fidelity Asset Manager: Income* Mutual fund 294,045 shares 3,547,970 3,581,467 Fidelity U.S. Bond Index Portfolio* Mutual fund 424,490 shares 4,543,214 4,325,553 Fidelity Contrafund* Mutual fund 511,960 shares 26,740,730 30,727,829 Neuberger Berman Genesis Trust Mutual fund 30,651 shares 591,519 644,903 Participant loans* Interest rates from 9.43% to 11.87% - 10,065,484 *Party-in-interest. 9

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the trustees (or other persons who administer the employee benefit plan) have duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized. Amgen Retirement and Savings Plan (Name of Plan) Date: 6/16/00 By: /s/ Barry D. Schehr ------- --------------------------- Barry D. Schehr Vice President, Financial Operations, and Chief Accounting Officer Amgen Inc.

AMGEN RETIREMENT AND SAVINGS PLAN INDEX TO EXHIBIT Consent of Ernst & Young LLP, Independent Auditors Exhibit 1

EXHIBIT 1 CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS We consent to the incorporation by reference in the Registration Statement (Form S-8 No. 33-39104) pertaining to the Amgen Retirement and Savings Plan of our report dated May 26, 2000, with respect to the financial statements and supplemental schedule of the Amgen Retirement and Savings Plan included in this Annual Report (Form 11-K) for the year ended December 31, 1999. /s/ Ernst & Young LLP Los Angeles, California June 16, 2000