OBJECTIVE Chronic thrombo-embolic pulmonary hypertension is a rare and aberrant outcome of acute pulmonary embolism. Because it has become a potentially curable form of pulmonary hypertension, the frequency of recognized cases has increased. We report a case series of 70 patients with chronic thromboembolic pulmonary hypertension evaluated in our institution between 1984 and 1993, and discuss diagnostic clues and therapeutic approaches. RESULTS All patients complained of dyspnoea on exertion. A history of acute thrombo-embolic events and lung murmurs were found in 60% and 17% of patients respectively. Coagulation disorders were found in 30% of the patients tested; the most common abnormality was lupus anticoagulant. The key non-invasive study for diagnosis was the lung perfusion scan which showed at least one segmental or wider perfusion defects in all patients. Pulmonary angiography confirmed the diagnosis in all cases and, sometimes associated with intravascular ultrasound imaging, established the feasibility of thromboendarterectomy. Medical therapy included the use of long-term oral anticoagulant, and in case of lower limb venous thrombosis, inferior vena cava filtration. Finally two surgical procedures were discussed in selected patients: thromboendarterectomy and lung transplantation. Since 1988, eight patients have benefited from lung transplantation (six patients are still alive) and 11 patients underwent thromboendarterectomy which was successful in 9 patients leading to dramatic functional and haemodynamic improvement. CONCLUSIONS Chronic thrombo-embolic pulmonary hypertension is a severe, sometimes fatal, disease which can be successfully treated by pulmonary thromboendartectomy and lung transplantation.