International audience; Background: Chronic thromboembolic pulmonary hypertension (CTEPH) is a life-threatening pulmonary embolism's (PE) complication whose incidence and predictors are not precisely determined.Objective: To determine the frequency and predictors for CTEPH after a first unprovoked PE.Patients/methods: In a randomized trial comparing an additional 18-month warfarin versus placebo in patients after a first unprovoked PE initially treated with vitamin K antagonist for 6 months, we applied recommended CTEPH screening strategies through 8-year follow-up to determine cumulative incidence of CTEPH. CTEPH predictors were estimated using Cox models. Pulmonary vascular obstruction (PVO) and systolic pulmonary arterial pressure (sPAP) at PE diagnosis and 6 months were studied by receiver operating curves analysis. All CTEPH cases and whether they were incident or prevalent were adjudicated.Results: During a median follow-up of 8.7 years, 9 CTEPH cases were diagnosed among 371 patients, with a cumulative incidence of 2.8% (95% confidence interval [CI], 0.95-4.64), and of 1.31% (95%CI, 0.01-2.60) after exclusion of 5 cases adjudicated as prevalent. At PE diagnosis, PVO>45% and sPAP>56mmHg were associated with CTEPH with a hazard ratio (HR) of 33.00 (95%CI 1.64-667.00, p=0.02) and 12.50 (95%CI 2.10-74.80, p65 years, lupus anticoagulant antibodies and non-O blood groups were also predictive of CTEPH. PVO>14% and sPAP>34mmHg at 6-month were associated with CTEPH (HRs 63.90 [95%CI, 3.11-1310.00, p