Chronic thromboembolic pulmonary hypertension (CTEPH) is characterised by nonresolving pulmonary thromboemboli that can be treated by surgical pulmonary endarterectomy (PEA). The authors of the present study sought to confirm known and to identify novel CTEPH risk factors in a controlled retrospective cohort study of prevalent CTEPH cases collected in three European centres offering PEA.Data from CTEPH patients were compared with nonthromboembolic pre-capillary pulmonary arterial hypertension cohorts at the participating institutions.The study population comprised 687 patients assessed at the time of diagnosis between 1996 and 2007. Ventriculo-atrial shunts and infected pacemakers (odds ratio (OR) 76.40, 95% confidence interval (CI) 7.67-10,351), splenectomy (OR 17.87, 95% CI 1.56-2,438), previous venous thromboembolism (VTE; OR 4.52, 95% CI 2.35-9.12), recurrent VTE (OR 14.49, 95% CI 5.40-43.08), blood groups other than 0 (2.09, 95% CI 1.12-3.94), and lupus anticoagulant/ antiphospholipid antibodies (OR 4.20, 95% CI 1.56-12.21) were more often associated with CTEPH. Thyroid replacement therapy (OR 6.10, 95% CI 2.73-15.05) and a history of malignancy (OR 3.76, 95% CI 1.47-10.43) emerged as novel CTEPH risk factors.In conclusion, the European database study confirmed previous knowledge of chronic thromboembolic pulmonary hypertension risk factors, and identified thyroid replacement therapy and a history of malignancy as new medical conditions associated with chronic thromboembolic pulmonary hypertension.