<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-09-24</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000005272</issuerCik>
        <issuerName>AMERICAN INTERNATIONAL GROUP INC</issuerName>
        <issuerTradingSymbol>AIG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001236432</rptOwnerCik>
            <rptOwnerName>MATTHEWS EDWARDS E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>399 PARK AVENUE 17TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-09-24</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>82507</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.2742</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-09-24</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>23500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.2742</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8580850</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnote</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Prior to the transactions reported by this Form 4, Mr. Matthews? wife held 23,500 shares of American International Group, Inc. (?AIG?) common stock.  Mr. Matthews may be deemed to be the beneficial owner of and to have a pecuniary interest in the shares of AIG common stock held by his wife.  Mr. Matthews disclaims beneficial ownership of and any pecuniary interest in the shares of AIG common stock held by his wife.</footnote>
        <footnote id="F2">Mr. Matthews may be deemed to be the beneficial owner of and to have a pecuniary interest in the shares of AIG common stock held by the C. V. Starr &amp; Co., Inc. Trust (the ?CV Starr Trust?).  Mr. Matthews disclaims beneficial ownership of and any pecuniary interest in the shares of AIG common stock held by the CV Starr Trust.</footnote>
    </footnotes>

    <remarks>Mr. Matthews may be deemed to beneficially own more than 10% of the common stock of American International Group, Inc. under Rule 16a-1(a)(1) under the Securities Exchange Act of 1934, as amended (the &quot;Exchange Act&quot;), as a result of him being deemed a member of a group under Section 13(d)(3) of the Exchange Act.</remarks>

    <ownerSignature>
        <signatureName>/s/Mike F. Huang, Attorney-in-Fact</signatureName>
        <signatureDate>2008-09-24</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/Bertil P-H Lundqvist, Attorney-in Fact</signatureName>
        <signatureDate>2008-09-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
