<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

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

    <issuer>
        <issuerCik>0000356708</issuerCik>
        <issuerName>FIRST REGIONAL BANCORP</issuerName>
        <issuerTradingSymbol>FRGB</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001262632</rptOwnerCik>
            <rptOwnerName>THOMPSON ELIZABETH</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>Chief Financial Officer</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable><nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>996</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
<footnoteId id="F1"></footnoteId>
</directOrIndirectOwnership>
<natureOfOwnership><value>401K Plan</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>953</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
<footnoteId id="F2"></footnoteId>
</directOrIndirectOwnership>
<natureOfOwnership><value>Employee Stock Ownership Plan</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
</nonDerivativeTable>
<derivativeTable><derivativeHolding><securityTitle><value>Stock Option (right to buy)</value>
</securityTitle>
<conversionOrExercisePrice><value>7.25</value>
</conversionOrExercisePrice>
<exerciseDate><value>2002-01-20</value>
</exerciseDate>
<expirationDate><value>2005-01-20</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>1600</value>
</underlyingSecurityShares>
</underlyingSecurity>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding><securityTitle><value>Stock Option (right to buy)</value>
</securityTitle>
<conversionOrExercisePrice><value>7.25</value>
</conversionOrExercisePrice>
<exerciseDate><value>2003-01-20</value>
</exerciseDate>
<expirationDate><value>2005-01-20</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>800</value>
</underlyingSecurityShares>
</underlyingSecurity>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding><securityTitle><value>Stock Option (right to buy)</value>
</securityTitle>
<conversionOrExercisePrice><value>7.25</value>
</conversionOrExercisePrice>
<exerciseDate><value>2004-01-20</value>
</exerciseDate>
<expirationDate><value>2005-01-20</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>800</value>
</underlyingSecurityShares>
</underlyingSecurity>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding><securityTitle><value>Stock Option (right to buy)</value>
</securityTitle>
<conversionOrExercisePrice><value>7.25</value>
</conversionOrExercisePrice>
<exerciseDate><value>2004-07-20</value>
</exerciseDate>
<expirationDate><value>2005-01-20</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>800</value>
</underlyingSecurityShares>
</underlyingSecurity>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeHolding>
</derivativeTable>
<footnotes><footnote id="F1">Represents total number of shares in the 401K Plan as of 1/1/2003 (fully vested)</footnote>
<footnote id="F2">Represents total number of shares in Employee Stock Ownership Plan as of 1/1/2003 (381 shares vested at 1/1/2003)</footnote>
</footnotes>
<ownerSignature><signatureName>Elizabeth J. Thompson</signatureName>
<signatureDate>2003-09-24</signatureDate>
</ownerSignature>
</ownershipDocument>

