<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>3</documentType>
<periodOfReport>2003-07-01</periodOfReport>
    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000356708</issuerCik>
        <issuerName>FIRST REGIONAL BANCORP</issuerName>
        <issuerTradingSymbol>FRGB</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001262631</rptOwnerCik>
            <rptOwnerName>SWEENEY STEVEN J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1801 CENTURY PARK EAST</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LOS ANGELES</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>90067</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>0</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>EVP &amp; General Counsel (3)</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable><nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>47000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
</directOrIndirectOwnership>
<natureOfOwnership><value>As Beneficiary and Trustee of Stephen John Sweeney Irrevocable Trust</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>44800</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
<footnoteId id="F1"></footnoteId>
</directOrIndirectOwnership>
<natureOfOwnership><value>As Trustee of Cynthia McLean Irrevocable Trust</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>52000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
<footnoteId id="F1"></footnoteId>
</directOrIndirectOwnership>
<natureOfOwnership><value>As Trustee of Patricia Lynne Sweeney Irrevocable Trust</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>7001</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
<footnoteId id="F1"></footnoteId>
<footnoteId id="F2"></footnoteId>
</directOrIndirectOwnership>
<natureOfOwnership><value>By Nicholas Akira Sweeney Irrevocable Trust</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>1402</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
<footnoteId id="F1"></footnoteId>
<footnoteId id="F2"></footnoteId>
</directOrIndirectOwnership>
<natureOfOwnership><value>By Jaclyn Yuki Sweeney Irrevocable Trust</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
</nonDerivativeTable>
<derivativeTable></derivativeTable>
<footnotes><footnote id="F1">The reporting person disclaims beneficial ownership of these shares, and this report shall not be deemed an admission that the reporting person is a beneficial owner of such shares for purposes of Section 16 or for any other purpose.</footnote>
<footnote id="F2">Shares beneficially owned by minor child.</footnote>
</footnotes>
<remarks>(3) The reporting person, an officer of a subsidiary of the issuer, may be deemed to be an officer of the issuer pursuant to Rule16a-1(f) under the Securities Exchange Act of 1934.</remarks>
<ownerSignature><signatureName>Steven J. Sweeney</signatureName>
<signatureDate>2003-09-24</signatureDate>
</ownerSignature>
</ownershipDocument>

