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

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2004-05-12</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001142596</issuerCik>
        <issuerName>NUVASIVE INC</issuerName>
        <issuerTradingSymbol>NUVA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001242721</rptOwnerCik>
            <rptOwnerName>KPCB VII ASSOCIATES LP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2750 SAND HILL ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MENLO PARK</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94025</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Series A Preferred Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>112500</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">Immediately following the closing of the initial public offering of the Issuer's Common Stock, all outstanding shares of Preferred Stock will be automatically converted into shares of the Issuer's Common Stock.</footnote>
        <footnote id="F2">KPCB VII Associates, L.P., a California limited partnership (&quot;KPCB VII Associates&quot;) is the general partner of KPCB Life Sciences Zaibatsu Fund II, L.P., a California limited partnership (&quot;KPCB Life&quot;).  KPCB VII Associates disclaims beneficial ownership of these shares held directly by KPCB Life, except to the extent of any indirect pecuniary interest in their distributive share therein.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Joseph S. Lacob, general partner</signatureName>
        <signatureDate>2004-05-12</signatureDate>
    </ownerSignature>
</ownershipDocument>

