<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:ns2="http://www.sec.gov/edgar/common">
    <headerData>
        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001801372</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



        </filerInfo>
    </headerData>
    <formData>
        <issuerInfo>
            <issuerCik>0001649904</issuerCik>
            <issuerName>RHYTHM PHARMACEUTICALS INC</issuerName>
            <secFileNumber>001-38223</secFileNumber>
            <issuerAddress>
                <ns2:street1>222 Berkeley Street </ns2:street1>
                <ns2:city>BOSTON</ns2:city>
                <ns2:stateOrCountry>MA</ns2:stateOrCountry>
                <ns2:zipCode>02116</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>8572644293</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>JENNIFER CHIEN</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>38th Fl.</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>6166</noOfUnitsSold>
            <aggregateMarketValue>171414.80</aggregateMarketValue>
            <noOfUnitsOutstanding>56901530</noOfUnitsOutstanding>
            <approxSaleDate>09/05/2023</approxSaleDate>
            <securitiesExchangeName>NASDAQ</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>09/05/2023</acquiredDate>
            <natureOfAcquisitionTransaction>Exercise of Stock Options</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>4519</amountOfSecuritiesAcquired>
            <paymentDate>09/05/2023</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>02/09/2023</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock Units</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>1647</amountOfSecuritiesAcquired>
            <paymentDate>02/09/2023</paymentDate>
            <natureOfPayment>N/A</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>10b5-1 Sales for JENNIFER CHIEN</name>
                <address>
                    <ns2:street1>222 Berkeley Street </ns2:street1>
                    <ns2:city>BOSTON</ns2:city>
                    <ns2:stateOrCountry>MA</ns2:stateOrCountry>
                    <ns2:zipCode>02116</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>08/09/2023</saleDate>
            <amountOfSecuritiesSold>1718</amountOfSecuritiesSold>
            <grossProceeds>42365.88</grossProceeds>
        </securitiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>10b5-1 Sales for JENNIFER CHIEN</name>
                <address>
                    <ns2:street1>222 Berkeley Street </ns2:street1>
                    <ns2:city>BOSTON</ns2:city>
                    <ns2:stateOrCountry>MA</ns2:stateOrCountry>
                    <ns2:zipCode>02116</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>08/07/2023</saleDate>
            <amountOfSecuritiesSold>11223</amountOfSecuritiesSold>
            <grossProceeds>271347.45</grossProceeds>
        </securitiesSoldInPast3Months>
        <remarks>The securities to be sold were acquired upon the vesting of restricted stock units during the period of 02/09/2023 through 02/11/2022
</remarks>
        <noticeSignature>
            <noticeDate>09/05/2023</noticeDate>
            <planAdoptionDates>
                <planAdoptionDate>05/08/2023</planAdoptionDate>
            </planAdoptionDates>
            <signature>/s/ Jennifer Chien</signature>
        </noticeSignature>
    </formData>
</edgarSubmission>
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144
0001801372
XXXXXXXX
LIVE
0001649904
RHYTHM PHARMACEUTICALS INC
001-38223
222 Berkeley Street
BOSTON
MA
02116
8572644293
JENNIFER CHIEN
Officer
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Fl.
New York
NY
10004
6166
171414.80
56901530
09/05/2023
NASDAQ
Common
09/05/2023
Exercise of Stock Options
Issuer
N
4519
09/05/2023
Cash
Common
02/09/2023
Restricted Stock Units
Issuer
N
1647
02/09/2023
N/A
N
10b5-1 Sales for JENNIFER CHIEN
222 Berkeley Street
BOSTON
MA
02116
Common
08/09/2023
1718
42365.88
10b5-1 Sales for JENNIFER CHIEN
222 Berkeley Street
BOSTON
MA
02116
Common
08/07/2023
11223
271347.45
The securities to be sold were acquired upon the vesting of restricted stock units during the period of 02/09/2023 through 02/11/2022
09/05/2023
05/08/2023
/s/ Jennifer Chien