<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2004-01-15</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000356708</issuerCik>
        <issuerName>FIRST REGIONAL BANCORP</issuerName>
        <issuerTradingSymbol>FRGB</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001068904</rptOwnerCik>
            <rptOwnerName>SWEENEY JACK A</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>1</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>1</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>Chairman &amp; CEO</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable><nonDerivativeTransaction><securityTitle><value>Common Stock</value>
</securityTitle>
<transactionDate><value>2004-01-15</value>
</transactionDate>
<transactionCoding><transactionFormType>4</transactionFormType>
<transactionCode>D</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionAmounts><transactionShares><value>10000</value>
</transactionShares>
<transactionPricePerShare><value>28.05</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode><value>D</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>668905</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
<footnoteId id="F1"></footnoteId>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeTransaction>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>281400</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>100000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
<footnoteId id="F2"></footnoteId>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeHolding>
<nonDerivativeHolding><securityTitle><value>Common Stock</value>
</securityTitle>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>31695</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>I</value>
<footnoteId id="F3"></footnoteId>
</directOrIndirectOwnership>
<natureOfOwnership><value>401K Plan</value>
</natureOfOwnership>
</ownershipNature>
</nonDerivativeHolding>
</nonDerivativeTable>
<derivativeTable><derivativeHolding><securityTitle><value>Stock Option (right to buy)</value>
</securityTitle>
<conversionOrExercisePrice><value>20.79</value>
</conversionOrExercisePrice>
<exerciseDate><value>2004-10-01</value>
<footnoteId id="F4"></footnoteId>
</exerciseDate>
<expirationDate><value>2013-09-01</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>26000</value>
<footnoteId id="F4"></footnoteId>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>126000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeHolding>
<derivativeHolding><securityTitle><value>Stock Option (right to buy)</value>
</securityTitle>
<conversionOrExercisePrice><value>11.50</value>
</conversionOrExercisePrice>
<exerciseDate><value>2002-12-31</value>
<footnoteId id="F5"></footnoteId>
</exerciseDate>
<expirationDate><value>2012-11-01</value>
</expirationDate>
<underlyingSecurity><underlyingSecurityTitle><value>Common Stock</value>
</underlyingSecurityTitle>
<underlyingSecurityShares><value>100000</value>
<footnoteId id="F5"></footnoteId>
</underlyingSecurityShares>
</underlyingSecurity>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>126000</value>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</derivativeHolding>
</derivativeTable>
<footnotes><footnote id="F1">Shares beneficially owned by reporting person through Trust A-1 of the Sweeney Family Trust U/I 11/13/98, a revocable trust of which the reporting person is the settler, sole trustee and sole beneficiary.</footnote>
<footnote id="F2">Shares beneficially owned by reporting person with Marilyn J. Sweeney, the reporting person's spouse, through Trust B of the Sweeney Family Trust U/I 11/13/98.</footnote>
<footnote id="F3">Represents total number of shares in 401K Plan as of January 15, 2004, all of which are fully vested.</footnote>
<footnote id="F4">The option was granted on September 22, 2003 under the company's 1999 Stock Option Plan and vests over seven years as follows:  3,714 option shares on October 1 of 2004, 2005, 2006, 2007, 2008 and 2009 and 3,716 shares on October 1, 2010.</footnote>
<footnote id="F5">The option was granted on November 12, 2002 under the company's 1999 Stock Option Plan and vests over five years, as follows:  50,000 option shares on December 31, 2002, and 10,000 option shares on December 31 of 2003, 2004, 2005, 2006 and 2007.</footnote>
</footnotes>
<remarks>6.  Power of attorney filed as Exhibit 24 to reporting persons's Form 4, filed 9/24/2003.</remarks>
<ownerSignature><signatureName>Steven J. Sweeney, attorney-in-fact for Jack A. Sweeney</signatureName>
<signatureDate>2004-01-16</signatureDate>
</ownerSignature>
</ownershipDocument>

