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

    <schemaVersion>X0407</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2023-04-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000872912</issuerCik>
        <issuerName>DELCATH SYSTEMS, INC.</issuerName>
        <issuerTradingSymbol>DCTH</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001622627</rptOwnerCik>
            <rptOwnerName>Rosalind Advisors, Inc.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>15 WELLESLEY STREET WEST</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 326</rptOwnerStreet2>
            <rptOwnerCity>TORONTO</rptOwnerCity>
            <rptOwnerState>A6</rptOwnerState>
            <rptOwnerZipCode>M4Y 0G7</rptOwnerZipCode>
            <rptOwnerStateDescription>ONTARIO, CANADA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001623082</rptOwnerCik>
            <rptOwnerName>SALAMON STEVEN A J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>15 WELLESLEY STREET WEST</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 326</rptOwnerStreet2>
            <rptOwnerCity>TORONTO</rptOwnerCity>
            <rptOwnerState>A6</rptOwnerState>
            <rptOwnerZipCode>M4Y 0G7</rptOwnerZipCode>
            <rptOwnerStateDescription>ONTARIO, CANADA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001811824</rptOwnerCik>
            <rptOwnerName>Aharon Gil</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>15 WELLESLEY STREET WEST</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 326</rptOwnerStreet2>
            <rptOwnerCity>TORONTO</rptOwnerCity>
            <rptOwnerState>A6</rptOwnerState>
            <rptOwnerZipCode>M4Y 0G7</rptOwnerZipCode>
            <rptOwnerStateDescription>ONTARIO, CANADA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Pre-Funded Warrant</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0.01</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2023-04-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>H</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>538828</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.63</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2022-09-07</value>
            </exerciseDate>
            <expirationDate>
                <value>2032-07-20</value>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>DELCATH SYSTEMS, INC. COMMON</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>538828</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>719965</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Rosalind Advisors, Inc., the advisor to the Rosalind Funds</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Each Reporting Persons disclaims beneficial ownership over the shares except to the extent of his or its respective pecuniary interest therein.</footnote>
        <footnote id="F2">The holder of the prefunded warrant is entitled to purchase the COMMON SHARES underlying the warrant from the initial exercise date UNTIL THIS Warrant is exercised in full as defined in the Form of Warrant.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>STEVEN SALAMON</signatureName>
        <signatureDate>2023-04-20</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>STEVEN SALAMON</signatureName>
        <signatureDate>2023-04-20</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>GIL AHARON</signatureName>
        <signatureDate>2023-04-20</signatureDate>
    </ownerSignature>
</ownershipDocument>
