SECURITIES AND EXCHANGE COMMISSION

Form 10-K

Commission file number 1-8787

American International Group, Inc.

Registrant’s telephone number, including area code (212) 770-7000

Securities registered pursuant to Section 12(b) of the Act:

Securities registered pursuant to Section 12(g) of the Act:

    Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes ü                    No              

    Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. o

    Indicate by check mark whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Exchange Act).    Yes ü                    No             

    The aggregate market value of the voting and nonvoting common equity held by nonaffiliates of the registrant computed by reference to the price at which the common equity was last sold as of June 30, 2003 (the last business day of the registrant’s most recently completed second fiscal quarter), was approximately $115,958,906,000.

    As of January 31, 2004, there were outstanding 2,608,947,657 shares of Common Stock, $2.50 par value per share, of the registrant.

Documents Incorporated by Reference:

    The registrant’s definitive proxy statement filed or to be filed with the Securities and Exchange Commission pursuant to Regulation 14A involving the election of directors at the annual meeting of the shareholders of the registrant scheduled to be held on May 19, 2004 is incorporated by reference in Part III of this Form 10-K.

PART I

American International Group, Inc. (AIG), a Delaware corporation, is a holding company, which through its subsidiaries, is engaged in a broad range of insurance and insurance-related activities in the United States and abroad. AIG’s primary activities include both General and Life Insurance operations. Other significant activities include Financial Services, and Retirement Services & Asset Management. The principal General Insurance company subsidiaries are American Home Assurance Company (American Home), National Union Fire Insurance Company of Pittsburgh, Pa. (National Union), New Hampshire Insurance Company (New Hampshire), Lexington Insurance Company (Lexington), The Hartford Steam Boiler Inspection and Insurance Company (HSB), Transatlantic Reinsurance Company, American International Underwriters Overseas, Ltd. (AIUO) and United Guaranty Residential Insurance Company. Significant Life Insurance operations include those conducted through American Life Insurance Company (ALICO), American International Reinsurance Company, Ltd. (AIRCO), American International Assurance Company, Limited together with American International Assurance Company (Bermuda) Limited (AIA), Nan Shan Life Insurance Company, Ltd. (Nan Shan), AIG Star Life Insurance Co., Ltd. (AIG Star Life), AIG Annuity Insurance Company (AIG Annuity), the AIG American General Life Companies (AIG American General), and SunAmerica Life Insurance Company (SunAmerica Life). AIG’s Financial Services operations are conducted primarily through International Lease Finance Corporation (ILFC), AIG Financial Products Corp. and its subsidiaries (AIGFP), and American General Finance, Inc. and its subsidiaries (AGF), while Retirement Services & Asset Management operations include The Variable Annuity Life Insurance Company (VALIC), AIG SunAmerica Asset Management Corp. (SAAMCo), AIG SunAmerica Life Assurance Company and AIG Global Asset Management Holdings Corp. (formerly known as AIG Global Investment Group, Inc.) and its subsidiaries and affiliated companies (AIG Global Investment Group).

     On August 29, 2001, AIG acquired American General Corporation (AGC). In connection with the acquisition, AIG issued approximately 290 million shares of common stock, $2.50 par value per share (common stock) in an exchange for all the outstanding common stock of AGC based on an exchange ratio of 0.5790 of a share of AIG common stock for each share of AGC common stock. The acquisition was accounted for as a pooling of interests and all prior historical financial information presented herein has been restated to include AGC. For information on AIG’s business segments, see Note 2 of Notes to Financial Statements.

     All per share information herein gives retroactive effect to all stock dividends and stock splits. As of January 31, 2004, beneficial ownership of approximately 11.9 percent, 2.0 percent and 1.8 percent of AIG common stock, was held by Starr International Company, Inc. (SICO), The Starr Foundation and C.V. Starr & Co., Inc. (Starr), respectively.

     At December 31, 2003, AIG and its subsidiaries had approximately 86,000 employees.

     AIG’s Internet address for its corporate website is www.aigcorporate.com. AIG makes available free of charge, on or through the Investor Information section of AIG’s corporate website, Annual Reports on Form 10-K, Quarterly Reports on Form 10-Q and Current Reports on Form 8-K and amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 as soon as reasonably practicable after such materials are electronically filed with, or furnished to, the Securities and Exchange Commission (SEC).

     Throughout this Annual Report on Form 10-K, AIG presents its operations in the way it believes will be most meaningful, as well as most transparent. Certain of the measurements used by AIG management are “non-GAAP financial measures” under SEC rules and regulations. Gross premiums written, statutory underwriting profit (loss) and combined ratios are presented in accordance with accounting principles prescribed by insurance regulatory authorities. For an explanation of why AIG management considers these “non-GAAP measures” useful to investors, see Management’s Discussion and Analysis of Financial Condition and Results of Operations.

The following table shows the general development of the business of AIG on a consolidated basis, the contributions made to AIG’s consolidated revenues and operating income and the assets held, in the periods indicated, by its General Insurance, Life Insurance, Financial Services, and Retirement Services & Asset Management operations and other realized capital gains (losses). (See also Management’s Discussion and Analysis of Financial Condition and Results of Operations and Notes 1 and 2 of Notes to Financial Statements.)

The following table shows identifiable assets, revenues and income derived from operations in the United States and Canada and from operations in other countries for the year ended December 31, 2003. (See also Note 2 of Notes to Financial Statements.)

 General Insurance Operations

AIG’s General Insurance subsidiaries are multiple line companies writing substantially all lines of property and casualty insurance. Domestic General Insurance operations are comprised of the Domestic Brokerage Group (DBG), which includes the operations of HSB; Transatlantic Holdings, Inc. (Transatlantic); Personal Lines, including 21st Century Insurance Group (21st Century); and United Guaranty Corporation (UGC).

     AIG’s primary domestic division is DBG. DBG’s business is derived from brokers in the United States and Canada and is conducted through its General Insurance subsidiaries including American Home, National Union, Lexington and certain other General Insurance company subsidiaries of AIG. The AIG Risk Management operation provides insurance and risk management programs for large corporate customers. The AIG Risk Finance division designs and implements risk financing alternatives using the insurance and financial services capabilities of AIG. Also included in DBG are the operations of AIG Environmental, which focuses specifically on providing specialty products to clients with environmental exposures.

     DBG writes substantially all classes of business insurance accepting such business mainly from insurance brokers. This provides DBG the opportunity to select specialized markets and retain underwriting control. Any licensed broker is able to submit business to DBG without the traditional agent-company contractual relationship, but such broker usually has no authority to commit DBG to accept a risk.

     In addition to writing substantially all classes of business insurance, including large commercial or industrial property insurance, excess liability, inland marine, environmental, workers’ compensation and excess and umbrella coverages, DBG offers many specialized forms of insurance such as equipment breakdown, directors and officers liability, difference-in-conditions, kidnap-ransom, export credit and political risk, and various types of professional errors and omissions coverages. Lexington writes surplus lines, those risks for which conventional insurance companies do not readily provide insurance coverage, either because of complexity or because the coverage does not lend itself to conventional contracts.

     Transatlantic offers reinsurance capacity on both treaty and facultative basis. Transatlantic structures programs for a full range of property and casualty products with an emphasis on specialty risk.

     AIG engages in mass marketing of personal lines coverages, primarily private passenger auto and personal umbrella coverages, principally through American International Insur-

     The business of UGC and its subsidiaries is also included in the domestic operations of AIG. The principal business of the UGC subsidiaries is the writing of residential mortgage loan insurance, which is guaranty insurance on conventional first mortgage loans on single-family dwellings and condominiums. Such insurance protects lenders against loss if borrowers default. UGC subsidiaries also write home equity and property improvement loan insurance on loans to finance residential property improvements, alterations and repairs and for other purposes not necessarily related to real estate. During 2003, UGC commenced providing guaranty insurance to providers of student loans. UGC had approximately $22 billion of guaranty risk in-force at December 31, 2003.

     AIG’s Foreign General insurance group accepts risks primarily underwritten through American International Underwriters (AIU), a marketing unit consisting of wholly owned agencies and insurance companies. The Foreign General insurance group also includes business written by AIG’s foreign-based insurance subsidiaries for their own accounts. The Foreign General group uses various marketing methods to write both business and personal lines insurance with certain refinements for local laws, customs and needs. AIU operates in Asia, the Pacific Rim, Europe, Africa, Middle East and Latin America.

     During 2003, DBG and the Foreign General insurance group accounted for 57.0 percent and 21.5 percent, respectively, of AIG’s General Insurance net premiums written.

     AIG’s General Insurance company subsidiaries worldwide operate primarily by underwriting and accepting risks for their direct account and securing reinsurance on that portion of the risk in excess of the limit which they wish to retain. This operating policy differs from that of many insurance companies which will underwrite only up to their net retention limit, thereby requiring the broker or agent to secure commitments from other underwriters for the remainder of the gross risk amount.

     The utilization of reinsurance is closely monitored by an internal reinsurance security committee, consisting of members of AIG’s senior management. No single reinsurer is a material reinsurer to AIG nor is AIG’s business substantially dependent upon any reinsurance contract. (See also Management’s Discussion and Analysis of Financial Condition and Results of Operations and Note 5 of Notes to Financial Statements.)

     AIG is diversified both in terms of lines of business and geographic locations. Of the General Insurance lines of business, workers’ compensation was approximately 12 percent of AIG’s net premiums written. This line of business is also diversified geographically.

     The majority of AIG’s General Insurance business is in the casualty classes, which tend to involve longer periods of time for the reporting and settling of claims. This may increase the risk and uncertainty with respect to AIG’s loss reserve development. (See also the Discussion and Analysis of Consolidated Net Losses and Loss Expense Reserve Development and Management’s Discussion and Analysis of Financial Condition and Results of Operations.)

Loss and expense ratios of AIG’s consolidated General Insurance operations are set forth in the following table. (See also Management’s Discussion and Analysis of Financial Condition and Results of Operations.)

     During 2003, of the direct General Insurance premiums written (gross premiums less return premiums and cancellations, excluding reinsurance assumed and before deducting reinsurance ceded), 11.0 percent, 7.6 percent and 6.4 percent were written in California, Illinois and New York, respectively. No other state accounted for more than 5 percent of such premiums.

     There was no significant adverse effect on AIG’s General Insurance results of operations from the economic environments in any one state, country or geographic region for the year ended December 31, 2003. (See also Management’s Discussion and Analysis of Financial Condition and Results of Operations.)

The reserve for net losses and loss expenses represents the accumulation of estimates for reported losses (“case basis reserves”) and provisions for losses incurred but not reported (IBNR), both reduced by applicable reinsurance recoverable. Losses and loss expenses are charged to income as incurred.

     Loss reserves established with respect to foreign business are set and monitored in terms of the respective local or functional currency. Therefore, no assumption is included for changes in currency rates. (See also Note 1(w) of Notes to Financial Statements.)

     Management reviews the adequacy of established loss reserves through the utilization of a number of analytical reserve development techniques. Through the use of these techniques, management is able to monitor the adequacy of its established reserves and determine appropriate assumptions for inflation. Also, analysis of emerging specific development patterns, such as case reserve redundancies or deficiencies and IBNR emergence, allows management to determine any required adjustments. (See also Management’s Discussion and Analysis of Financial Condition and Results of Operations.)

     The “Analysis of Consolidated Net Losses and Loss Expense Reserve Development Excluding Asbestos and Environmental Net Losses and Loss Expense Reserve Development” table, which follows, presents the development of net losses and loss expense reserves for calendar years 1993 through 2003. The upper half of the table shows the cumulative amounts paid during successive years related to the opening loss reserves. For example, with respect to the net losses and loss expense reserve of $19.66 billion as of December 31, 1996, by the end of 2003 (seven years later) $16.30 billion had actually been paid in settlement of these net loss reserves. In addition, as reflected in the lower section of the table, the original reserve of $19.66 billion was reestimated to be $19.11 billion at December 31, 2003. This decrease from the original estimate would generally be a combination of a number of factors, including reserves being settled for smaller amounts than originally estimated. The original estimates will also be increased or decreased as more information becomes known about the individual claims and overall claim frequency and severity patterns. The redundancy (deficiency) depicted in the table, for any particular calendar year, shows the aggregate change in estimates over the period of years subsequent to the calendar year reflected at the top of the respective column heading. For example, the deficiency of $1.54 billion at December 31, 2003 related to December 31, 2002 net losses and loss expense reserves of $29.65 billion represents the cumulative amount by which reserves for 2002 and prior years have developed deficiently during 2003. The deficiency that has emerged in the last year can be attributed primarily to claims from accident years 1999 and 2000. The accident year emergence can be seen by comparing the respective developments in 2003 for each column’s loss reserve in the table below. For example, the liability associated with the year end 2000 loss reserves increased to $30.12 billion at year end 2003 from $28.26 billion at year end 2002, an increase of $1.86 billion in 2003. Thus, loss estimates for accident years 2000 and prior, which comprise the year end 2000 loss reserve, increased by $1.86 billion during 2003. Similarly, the table shows that the loss estimates for accident years 1999 and prior, which comprise the year end 1999 loss reserve, increased to $28.10 billion at year end 2003 from $26.95 billion at year end 2002, an increase of approximately $1.15 billion. This increase of $1.15 billion, as compared to the $1.86 billion increase in the 2000 column, indicates that accident year 2000 loss estimates increased by approximately $710 million during 2003, i.e. the difference between the respective $1.86 billion and $1.15 billion amounts. Similar calculations from the table below reveal that the accident year 1999 loss estimates increased approximately $600 million during 2003. Thus, loss estimates for accident years 1999 and 2000 increased by approximately $1.3 billion during 2003. Loss estimates also increased for accident years 1998 and prior, but by amounts small in comparison to 1999 and 2000. The primary cause of these higher loss estimates is higher than expected loss emergence in 2003. Loss development patterns utilized to test the reserves generally rely on the actual historical loss development patterns of prior accident years for each class of business. Accident years 1999 and 2000 exhibited significantly higher than normal loss development in the latest calendar year, thus creating the adverse developments noted above. The classes accounting for the majority of this higher than expected loss emergence in 2003 were excess casualty, directors and officers’ liability, and healthcare liability. It should be noted that loss estimates for accident years 2001 and 2002 did not develop adversely in 2003. Additionally, as shown in the table below, loss emergence from year end 1993, 1994, 1995 and 1996 has been favorable on an inception to date basis through year end 2003.

     The reserve for net losses and loss expenses with respect to Transatlantic and 21st Century are included only in the consolidated net losses and loss expenses commencing with the year ended December 31, 1998. Reserve development for these operations is included only for the 1998 and subsequent periods. Thus, the comparisons for 1997 and prior year ends are not fully comparable to those for 1998 and subsequent in the table below.

The following table excludes for each calendar year the net loss and loss expense reserves and the development thereof with respect to asbestos and environmental claims. (See also Management’s Discussion and Analysis of Financial Condition and Results of Operations.)

The following table includes for each calendar year the net loss and loss expense reserves and the development thereof with respect to asbestos and environmental claims. (See also Management’s Discussion and Analysis of Financial Condition and Results of Operations.)