The aim of the open label extension (OLE) of CTREPH study was to characterize multimodal treatment in patients with severe inoperable CTEPH, to describe long-term subcutaneous (SC) treprostinil safety and tolerability, and to evaluate change in functional class and exercise capacity over 24 months since completion of the blinded phase of CTREPH. The target population in the OLE consisted of patients who completed 24 weeks of blinded treatment with either high-dose treprostinil of around 30 ng/kg/min (former high-dose group), or low-dose treprostinil of around 3 ng/kg/min (former low-dose group) in the CTREPH study. From the start of OLE, treprostinil dose and any additional therapy were chosen according to the standard of care and physician's discretion. Out of 47 enrolled patients, 20 patients received other PH drugs during OLE and 17 patients underwent at least 1 BPA session. Number of treprostinil-related AEs was substantially higher in the former low-dose group in comparison to the former high-dose group. Related AEs were also more frequent during the first 6 months of the preceding blinded trial than over 24 months of OLE, especially infusion site pain and all local infusion site reactions. No new safety signal was detected. Evaluated clinical outcomes show sustained benefit from long-term treprostinil treatment. Long-term SC treprostinil is a safe and effective component of multimodal treatment for patients with severe CTEPH. Patients who tolerate treprostinil after initiation are likely to continue tolerating it over time, with the clinical benefit maintained over 24 months.