Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare complication of pulmonary embolism. As for most rare diseases, epidemiologic data are scarce, but recent registries suggest an incidence of at least 5 per million inhabitants per year. A history of massive or recurrent acute pulmonary embolism is observed in most patients with CTEPH, but the proportion of patients who develop CTEPH after acute pulmonary embolism is a matter of debate, further complicated by the possible misdiagnosis of CTEPH as acute pulmonary embolism. A complete resolution of thrombi is usually not achieved after acute pulmonary embolism, and the clinical relevance of a “postpulmonary embolism syndrome” with persistent perfusion defects and exercise intolerance is discussed. Risk factors most consistently associated with CTEPH are circulating anti-phospholipid antibodies or lupus anticoagulant, increased factor VIII, non-O blood groups, and chronic inflammatory diseases. There is no female predominance, and it is a disease of older age. Survival in the absence of specific surgical or medical treatment is poor and depends on the hemodynamic severity.