Background: The phase 2b Riociguat Safety and Efficacy in Patients with Diffuse Cutaneous Systemic Sclerosis (RISE-SSc) trial investigated riociguat versus placebo in early diffuse cutaneous systemic sclerosis. The long-term extension evaluated safety and exploratory treatment effects for an additional year., Methods: Patients were enrolled to RISE-SSc between Jan 15, 2015, and Dec 8, 2016. Those who completed the 52-week, randomised, parallel-group, placebo-controlled, double-blind phase were eligible for the long-term extension. Patients originally assigned to riociguat continued therapy (riociguat-riociguat group). Those originally assigned to placebo were switched to riociguat (placebo-riociguat group), adjusted up to 2·5 mg three times daily in a 10-week, double-blind dose-adjustment phase, followed by an open-label phase. Statistical analyses were descriptive. Safety including adverse events and serious adverse events was assessed in the long-term safety analysis set (all patients randomly assigned and treated with study medication in the double-blind phase who continued study medication in the long-term extension). The RISE-SSc trial is registered with ClinicalTrials.gov, NCT02283762., Findings: In total, 87 (72%) of 121 patients in the main RISE-SSc study entered the long-term extension (riociguat-riociguat, n=42; placebo-riociguat, n=45). 65 (75%) of 87 patients were women, 22 (25%) were men, and 62 (71%) were White. Overall, 82 (94%) of 87 patients in the long-term extension had an adverse event; most (66 [76%] of 87) were of mild to moderate severity, with no increase in pulmonary-related serious adverse events in patients with interstitial lung disease., Interpretation: No new safety signals were observed with long-term riociguat in patients with early diffuse cutaneous systemic sclerosis. Study limitations include the absence of a comparator group in this open-label extension study., Funding: Bayer and Merck Sharp & Dohme., Competing Interests: Declaration of interests OD has or had consultancy relationships with and/or has received research funding from, or has served as a speaker in the area of potential treatments for systemic sclerosis and its complications in the last 3 years for AbbVie, Acceleron, Amgen, AnaMar, Arxx Therapeutics, Baecon, Bayer, Blade, Boehringer Ingelheim, ChemomAb, Corbus, CSL Behring, Galapagos, GSK, Glenmark, Horizon (Curzion), Inventiva, iQvia, Italfarmaco, Kymera, Medac, Medscape, Merck Sharp & Dohme, Mitsubishi Tanabe, Novartis, Pfizer, Roche, Roivant, Sanofi, Serodapharm, Target Bioscience, Topadur, and UCB. OD is named on a patent issued for “mir-29 for the treatment of systemic sclerosis” (US8247389, EP2331143). YA reports personal fees from Actelion, Bayer, and Boehringer Ingelheim; grants and personal fees from Bristol Myers Squibb; and grants from Inventiva, Roche, and Sanofi, outside the submitted work. CPD reports grants and personal fees from Arxx Therapeutics, CSL Behring, GSK, and Inventiva; grants from Servier; and personal fees from Acceleron, Bayer, Corbus, Galapagos, Horizon, Roche, and Sanofi Aventis. MK reports grants and personal fees from Boehringer Ingelheim, MBL, and Ono Pharmaceuticals; and personal fees from AbbVie, Asahi Kasei Pharma, Bayer, Chugai Pharmaceutical, Corbus, GSK, Horizon, Janssen, Mitsubishi Tanabe, Mochida, and Nippon Shinyaku, outside the submitted work. MM-C has received consulting fees or honoraria from Acceleron, Actelion, Bayer, Biogen, Boehringer Ingelheim, Chemomab, Corbus, CSL Behring, Galapagos, Inventiva, Janssen, Lilly, Mitsubishi, MSD, Novartis, Pfizer, Regeneron, Roche, Sandoz, Sanofi, Samsung, and UCB. JEP reports personal fees from AbbVie, Actelion, Amgen, Bayer, Bristol Myers Squibb, Lilly Pharmaceutical, Merck Sharp & Dohme, Novartis, Pfizer, Roche, Sandoz, Sanofi, and UCB, outside the submitted work. TA reports grants and personal fees from Astellas, Chugai, Daiichi-Sankyo, Mitsubishi Tanabe, Pfizer, and Takeda; grants from Alexion, Asahi Kasei, Bayer, Bristol Myers Squibb, Eisai, Otuska, and Takeda; and personal fees from Lilly, Ono Pharmaceutical, and Sanofi, outside the submitted work. LC reports personal fees from Actelion, Bayer, Boehringer Ingelheim, Lilly, Medac, Novartis, Pfizer, and Roche-Genentech, outside the submitted work. EH reports grants and personal fees from Actelion and GSK; and personal fees from Boehringer Ingelheim, Roche, and Sanofi-Genzyme. TI reports personal fees from AbbVie, Asahi Kasei Pharma, Astellas, Ayumi Pharmaceutical, Bristol Myers Squibb, Chugai Pharmaceutical, Daiichi-Sankyo, Eisai, Janssen, Mitsubishi Tanabe, Ono Pharmaceutical, Pfizer, and Sanofi, outside the submitted work. SRJ was a site investigator for trials sponsored by Boehringer Ingelheim and Corbus; and served on advisory boards sponsored by Boehringer Ingelheim and Ikaria. EDL reports consultancy relationships with Boehringer Ingelheim. ES has received grants and research support from Bayer. RMS has received research funding from Boehringer Ingelheim; and has served as a consultant for Boehringer Ingelheim, Corbus, Forbius, and Medtelligence. VSm reports grant/research support from the Belgian Fund for Scientific Research (FWRO), Boehringer Ingelheim Pharma, Janssen-Cilag, and the Research Foundation Flanders (FWO); consultancy for Boehringer Ingelheim Pharma, and Janssen-Cilag; and speaker fees from Actelion, Boehringer Ingelheim Pharma, Janssen-Cilag, and UCB. VSt reports participation in advisory boards, consultancy for economics of scleroderma management, and clinical trials for Bayer; investigator-initiated grants, advisory boards, and steering committees (consulting) for CSL Behring; participation in advisory boards and site primary investigator (PI) of clinical trials for Roche; site PI of clinical trials for the Immune Tolerance Network and Sanofi; and participation on a data safety monitoring board for an open-label phase 2 trial and site PI for a phase 3 trial for Corbus. WS reports speaker fees, advisory board fees, and research grants from Janssen; advisory board fees from Boehringer Ingelheim; and research grants from GSK. GS reports personal fees from Berlin-Chemie/A. Menarini, Boehringer Ingelheim, CSL Behring, Janssen-Cilag, Eli Lilly, Novartis, Pfizer, Roche-Genentech, and Sager Pharma, outside the submitted work. M-ET has or had consultancy relationships with and/or has received research funding from or has served as a speaker in the area of potential treatments for systemic sclerosis and its complications in the last 3 years for Boehringer Ingelheim, Gilead Galapagos, Glenmark, Lilly, and Medac. MW is an employee of Bayer. KL was an employee of StanFinn, which was partly insourced to Bayer during the conduct of the trial and is now an employee of Bayer. FK is an employee of and holds shares in Bayer. DK reports personal fees from Acceleron, Actelion, Boehringer Ingelheim, Corbus, CSL Behring, Roche-Genentech, Horizon, Mitsubishi Tanabe Pharma, and Talaris Therapeutics; and is Chief Medical Officer of Eicos Sciences, a subsidiary of CiviBioPharma, where he has stock options. All other authors declare no competing interests., (Copyright © 2023 Elsevier Ltd. All rights reserved.)