UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

FORM 8-K

CURRENT REPORT
Pursuant to Section 13 or 15(d) of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): February 7, 2005

Biogen Idec Inc.

Registrant’s telephone number, including area code: (617) 679-2000

Not Applicable
(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Table of Contents

ITEM 2.02 Results of Operations and Financial Condition.

     The press release attached as Exhibit 99.1 includes information with respect to the following: (a) the Registrant’s adjusted non-GAAP earnings per share and net income for the fourth quarter and full year 2004, and (b) the Registrant’s adjusted pro forma non-GAAP earnings per share, net income and revenues for the fourth quarter and full year 2003. These are non-GAAP financial measures.

     The non-GAAP financial measures for the fourth quarter and full year 2004 exclude merger-related impacts and other non-operating charges. The non-GAAP financial measures for the fourth quarter and full year 2003 include revenue and expenses from the former Biogen, Inc. and exclude merger-related impacts and other non-operating charges of the former Biogen, Inc. and former IDEC Pharmaceuticals Corporation.

     Management believes that the non-GAAP financial measures provide useful information to investors. In particular, management believes that they allow investors to monitor and evaluate the Registrant’s ongoing operating results and trends and gain a better understanding of the Registrant’s business, period-to-period performance, and prospects for future performance.

     This press release is being furnished pursuant to Item 2.02 of this Current Report on Form 8-K and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 (the “Exchange Act”) or otherwise subject to the liabilities of that Section, nor shall such documents be deemed incorporated by reference in any filing under the Securities Act of 1933 or the Exchange Act.

SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EXHIBIT INDEX

EXHIBIT 99.1

Page 1 Biogen Idec Reports Fourth Quarter and Full Year 2004 Earnings

Media Contact:
Jose Juves
Associate Director, Public Affairs
Biogen Idec
Tel: (617) 914-6524

Investment Community Contact:
Elizabeth Woo
Senior Director, Investor Relations
Biogen Idec
Tel: (617) 679-2812

FOR IMMEDIATE RELEASE

Biogen Idec Reports Fourth Quarter and Full Year 2004 Results

Cambridge, MA, February 7, 2005 — Biogen Idec Inc. (NASDAQ: BIIB), the world’s third largest biotech company with leading products and capabilities in oncology and immunology, today reported its fourth quarter and full year 2004 results.

Fourth Quarter & Full Year Highlights

Page 2 Biogen Idec Reports Fourth Quarter and Full Year 2004 Earnings

excluding merger-related accounting impacts and other non-operating charges, adjusted pro forma non-GAAP EPS were $0.34.

James Mullen, Biogen Idec’s Chief Executive Officer, commented, “Biogen Idec had a momentous year in 2004, highlighted by the approval of TYSABRI based on one-year data. Our major R&D programs experienced their most productive year and strong performance in AVONEX and RITUXAN fueled revenue growth of 19% to $2.2 billion. This puts us on track to meet our long-term goals of achieving approximately 15% top and 20% bottom line operating performance.”

Financial Performance

On an adjusted non-GAAP basis, Biogen Idec reported net income of $121 million in the fourth quarter of 2004 (Q4 2003 adjusted pro forma non-GAAP: $91 million) and $518 million for the full year 2004 (2003 adjusted pro forma non-GAAP: $432 million). Adjusted non-GAAP EPS was $0.34 for the fourth quarter of 2004 (Q4 2003 adjusted pro forma non-GAAP: $0.25) and $1.44 for the full year 2004 (2003 adjusted pro forma non-GAAP: $1.22).

These adjustments are itemized on the attached reconciliation tables. Adjusted non-GAAP EPS and net income for the fourth quarter and full year of 2004 exclude merger-related accounting impacts, such as amortization of intangibles, impairment of intangibles, inventory step up, and other merger-related charges, and other non-operating charges. Adjusted pro forma non-GAAP EPS and net income for the fourth quarter and full year of 2003 include revenue and expenses from the former Biogen, Inc. from January 1 to November 12, 2003 (date of merger) but excludes similar merger-related accounting impacts excluded from fourth quarter and full year 2004 adjusted non-GAAP EPS and other non-operating charges of the former Biogen, Inc. and IDEC Pharmaceuticals Corporation.

On a reported basis, calculated in accordance with GAAP, Biogen Idec reported net income of $48 million (or EPS of $0.14) in the fourth quarter of 2004 and net income of $45 million (or EPS of $0.13) for the full year 2004. The difference between adjusted non-GAAP net income and EPS and GAAP net income and EPS in the fourth quarter and full year were primarily due to non-cash merger-related accounting impacts of $88 million and $656 million, respectively. Full year 2004 was also impacted by a $13 million write-down of certain investments.

Revenue Performance

Page 3 Biogen Idec Reports Fourth Quarter and Full Year 2004 Earnings

Revenues from AVONEX, Biogen Idec’s therapy for patients with relapsing forms of MS, increased 19 % in the fourth quarter to $370 million (Q4 2003 adjusted pro forma non-GAAP: $310 million). Full year AVONEX sales increased 21 % to $1.42 billion (2003 adjusted pro forma non-GAAP: $1.17 billion). In 2004, U.S. sales were $922 million and international sales were $495 million.

Revenues from AMEVIVE^Ò (alefacept), Biogen Idec’s treatment for moderate-to-severe chronic plaque psoriasis, were $10 million in the fourth quarter (Q4 2003 adjusted pro forma non-GAAP: $17 million) and $43 million for the full year (2003 adjusted pro forma non-GAAP: $40 million).

Revenues from ZEVALIN^Ò (ibritumomab tiuxetan), Biogen Idec’s radioimmunotherapeutic agent for relapsed or refractory low-grade, follicular or transformed B-cell non-Hodgkin’s lymphoma (NHL), were $8 million in the fourth quarter of 2004 (Q4 2003: $5 million) and $23 million for the full year (2003: $20 million).

Revenues from TYSABRI, Biogen Idec’s therapy for patients with relapsing forms of MS, were $3 million in the fourth quarter.

Revenues for the fourth quarter of 2004 and full year 2004 included $170 million (Q4 2003: $130 million) and $615 million (2003: $493 million), respectively, from Biogen Idec’s joint business arrangement with Genentech, Inc. related to RITUXAN, a treatment for certain B-cell non-Hodgkin’s lymphomas that Biogen Idec co-promotes in the U.S. with Genentech. All U.S. sales of RITUXAN are recognized by Genentech, and Biogen Idec records its share of the pretax co-promotion profits on a quarterly basis. U.S. net sales of RITUXAN were $429 million in the fourth quarter (Q4 2003: $369 million) and $1.57 billion for the full year (2003: $1.36 billion), as reported by Genentech.

Royalties were $25 million in the fourth quarter (Q4 2003 adjusted pro forma non-GAAP: $27 million) and $98 million for the full year (2003 adjusted pro forma non-GAAP: $127 million).

Financial Guidance

Biogen Idec today reaffirmed its long-term goal of achieving 15% compound annual revenue growth, and approximately 20% compound annual earnings per share (adjusted pro forma non-GAAP) growth through 2007.

Given the launch investments behind TYSABRI, the Company is anticipating low double-digit growth for revenue and adjusted non-GAAP earnings in 2005. On this non-GAAP basis, the Company expects operating expenses to grow 12–14% over 2004 levels and its effective tax rate for 2005 to be in the range of 31–33%. As a result, the Company estimates that its 2005 non-GAAP earnings per share will be in the range of $1.60 to the low $1.70’s.

The Company anticipates that 2005 capital expenditures will be in the range of $400 — $475 million. A significant portion of these expenditures will be directed towards the

Page 4 Biogen Idec Reports Fourth Quarter and Full Year 2004 Earnings

completion of the Oceanside manufacturing facility and the construction of a large-scale manufacturing facility in Denmark.

Fourth Quarter 2004 Highlights

Conference Call and Webcast

The Company’s earnings conference call for the fourth quarter will be broadcast via the internet at 5:00 p.m. ET on February 7, 2005, and will be accessible through the investor relations section of Biogen Idec’s homepage, http://www.biogenidec.com.

Page 5 Biogen Idec Reports Fourth Quarter and Full Year 2004 Earnings

About Biogen Idec

Biogen Idec creates new standards of care in oncology and immunology. As a global leader in the development, manufacturing, and commercialization of novel therapies, Biogen Idec transforms scientific discoveries into advances in human healthcare. For product labeling, press releases and additional information about the company, please visit www.biogenidec.com.

Safe Harbor

This press release contains forward-looking statements regarding expected future financial results and plans for our development programs, including TYSABRI.

These statements are based on the Company’s current beliefs and expectations. A number of risks and uncertainties could cause actual results to differ materially. For example, financial results, including future revenue and EPS growth, anticipated levels of expenses, other statements regarding future financial performance, and overall prospects for the Company’s products may be affected by a number of factors, including the degree and timing of market acceptance of TYSABRI, any unexpected slowing of growth of the markets for AVONEX and RITUXAN, any change in market acceptance of these products in key markets worldwide, the impact of reimbursement and pricing decisions related to the Company’s products, particularly TYSABRI, the impact of competitive products on the Company’s products, any material decreases in sales by licensees of products on which the Company receives royalties, the impact of litigation, the impact of costs related to the launch of TYSABRI, any unanticipated increase in expenses related to in-licensing and product opportunities, increases in costs related to development of new products and existing products in new indications, and any material issues, delays or failures related to the manufacturing or supply of the Company’s products.

Drug development and commercialization involve a high degree of risk. For example, our development and commercialization of TYSABRI as a treatment for MS could be negatively affected if unexpected concerns arise from additional data, including the two-year data from the Phase 3 trial, once unblinded, or if we were to encounter other unexpected hurdles.

For more detailed information on the risks and uncertainties associated with these forward looking statements and the Company’s other activities see the periodic reports filed by the Company with the Securities and Exchange Commission. The Company does not undertake any obligation to publicly update any forward-looking statements, whether as a result of new information, future events, or otherwise.

TABLE 1
Financial Results For The Fourth Quarter and Full Year of 2004
Condensed Consolidated Statements Of Income — GAAP Basis
(in thousands, except per share amounts)

TABLE 2

Condensed Consolidated Balance Sheets
(dollars in thousands)

TABLE 3
Financial Results For The Fourth Quarter and Full Year 2004
Condensed Consolidated Statements Of Income — Operating Basis
(in millions, except per share amounts)

The non-GAAP financial measures presented below are utilized by Biogen Idec management to gain an understanding of the comparative financial performance of the Company. Management believes that the non-GAAP financial measures are useful because they exclude those non-operational activities or transactions that are not necessarily relevant to understanding the trends of the Company or the prospects of future performance. The presentation of this information is not meant to be considered in isolation or as a substitute for GAAP financial measures. Numbers may not foot due to rounding.

Adjustments were made to conform prior periods to current year presentation including adoption of EITF 03-06, which requires allocation of income to certain holders of equity and debt instruments and the immaterial correction of a non-GAAP elimination of intercompany activities between legacy pre-merger companies.

Table 4

Biogen Idec Inc
Product Revenues for Fourth Quarter and Full Year 2004
(in thousands)

The non-GAAP pro forma financial measures presented below are utilized by Biogen Idec management to gain an understanding of the comparative revenue performance of the Company. Management believes that the non-GAAP financial measures are useful because they include those non-GAAP activities or transactions that may be relevant to obtaining an understanding of the trends of the Company or the prospects of future performance.

(a) Represents former Biogen, Inc. revenue that is not included in GAAP revenues.