<ownershipDocument>
    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2003-12-02</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000911177</issuerCik>
        <issuerName>CASELLA WASTE SYSTEMS INC</issuerName>
        <issuerTradingSymbol>CWST</issuerTradingSymbol>
</issuer>
<reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001055352</rptOwnerCik>
            <rptOwnerName>CASELLA JOHN W</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O CASELLA WASTE SYSTEMS</rptOwnerStreet1>
            <rptOwnerStreet2>25 GREENS HILL LANE</rptOwnerStreet2>
            <rptOwnerCity>RUTLAND</rptOwnerCity>
            <rptOwnerState>VT</rptOwnerState>
            <rptOwnerZipCode>05701</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>Chief Executive Officer</officerTitle>
<otherText></otherText>
</reportingOwnerRelationship>
</reportingOwner>
<nonDerivativeTable><nonDerivativeTransaction><securityTitle><value>Class A Common Stock</value>
</securityTitle>
<transactionDate><value>2003-12-02</value>
</transactionDate>
<transactionCoding><transactionFormType>5</transactionFormType>
<transactionCode>G</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved>
</transactionCoding>
<transactionTimeliness><value>E</value>
</transactionTimeliness>
<transactionAmounts><transactionShares><value>10646</value>
</transactionShares>
<transactionPricePerShare><value>14.09</value>
</transactionPricePerShare>
<transactionAcquiredDisposedCode><value>D</value>
</transactionAcquiredDisposedCode>
</transactionAmounts>
<postTransactionAmounts><sharesOwnedFollowingTransaction><value>501494</value>
<footnoteId id="F1"></footnoteId>
</sharesOwnedFollowingTransaction>
</postTransactionAmounts>
<ownershipNature><directOrIndirectOwnership><value>D</value>
</directOrIndirectOwnership>
</ownershipNature>
</nonDerivativeTransaction>
</nonDerivativeTable>
<derivativeTable></derivativeTable>
<footnotes><footnote id="F1">In addition, indirect beneficial holdings of Mr. Casella consist of 57,468 shares of Class A Common Stock held in trust for the benefit of Mr. Casella's minor children, as well as 694 shares of Class A Common Stock held by Mr. Casella's wife.</footnote>
</footnotes>
<ownerSignature><signatureName>/s/ John W. Casella</signatureName>
<signatureDate>2003-12-10</signatureDate>
</ownerSignature>
</ownershipDocument>

