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Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 FORM 10 - K TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 Delaware ( State or other jurisdiction of incorporation or organization ) For the fiscal year ended December 31 , 2020 OR RHYTHM PHARMACEUTICALS , INC . ( Exact name of registrant as specified in its charter ) For the transition period from to Commission file number 001-38223 Title of each class Common Stock , $ 0.001 par value per share Securities registered pursuant to Section 12 ( b ) of the Act : 222 Berkeley Street th 12 Floor Boston , MA 02116 ( Address of principal executive offices ) ( Zip Code ) ( 857 ) 264-4280 ( Registrant's telephone number , including area code ) N / A ( Former name , former address and former fiscal year , if changed since last report ) Trading Symbol ( s ) 46-2159271 ( I.R.S. Employer Identification No. ) RYTM Name of each exchange on which registered The Nasdaq Stock Market LLC ( Nasdaq Global Market ) Securities registered pursuant to Section 12 ( g ) of the Act : None Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes No Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Act . Yes No X Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( § 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company , " and " emerging growth company " in Rule 12b - 2 of the Exchange Act . Large accelerated filer X Non - accelerated filer Accelerated filer Smaller reporting company Emerging growth company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . X Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No X. The aggregate market value of the voting and non - voting common equity held by non - affiliates of the registrant was approximately $ 828.1 million , based on the closing price of the registrant's Common Stock on June 30 , 2020 , the last business day of the registrant's most recently completed second fiscal quarter . Solely for purposes of this disclosure , Common Stock held by executive officers , directors and certain stockholders of the registrant as of such date have been excluded because such holders may be deemed to be affiliates . There were 50,181,164 shares of the registrant's Common Stock outstanding as of February 19 , 2021 . DOCUMENTS INCORPORATED BY REFERENCE The registrant intends to file a definitive proxy statement for the registrant's 2021 Annual Meeting of Stockholders within 120 days of the end of the fiscal year ended December 31 , 2020. Portions of such definitive proxy statement are incorporated by reference into Part III of this Annual Report on Form 10 - K .