Additional data on vasodilators and/or balloon pulmonary angioplasty (BPA) in patients with inoperable or persistent/recurrent CTEPH are important. The aim of our study was to evaluate safety and survival in severe CTEPH patients who received long-term subcutaneous (SC) treprostinil treatment in open label extension (OLE) of the randomized, double-blind, 24week CTREPH trial comparing high and low dose of SC treprostinil [Sadushi-Kolici R et al. Lancet Respir Med. 2019;Mar;7(3):239-48]. In OLE, dosing of SC treprostinil as well as any additional CTEPH therapy were at the investigatorsŽ decision. The OLE was completed after marketing authorization of treprostinil in April 2020. 47 patients participated in the OLE with mean OLE treatment duration of approximately 3 years (1132.4 ± 755.7 days). 20 patients underwent BPA. 15 patients received additional PH specific medication. During OLE, 3 patients started riociguat (1 in addition to macitentan) and 2 patients switched from sildenafil to riociguat. Overall survival was 93%, 87%, 84% after one, two and three years, respectively when 14 deaths were observed, all related to the underlying disease.77 adverse events (AEs) related to treprostinil were experienced by 27 patients, most commonly infusion site pain (19.5%), other infusion site reactions (31.2%) and diarrhoea (18.2%). 4 serious AEs (SAEs) related to treprostinil resolved without sequel. 4 patients discontinued treprostinil due to related AEs (3 infusion site pain and 1 headache). The OLE results confirm that long-term SC treprostinil is safe and effective component of multimodal treatment for patients with severe CTEPH.