Considerable progress has been made in the diagnosis and management of acute pulmonary thromboembolism (PTE) but there are few data about the true incidence, early mortality, and long term progress of this condition. Recurrent PTE or incomplete resolution of the initial event leading to the development of secondary pulmonary hypertension is even less well understood. In the UK the diagnosis of chronic thromboembolic pulmonary hypertension (CTEPH) remains infrequently considered and even less frequently confirmed. Many physicians remain unaware that the condition is potentially curable by corrective operation and rely on transplantation or palliative medical management. The incidence of acute pulmonary embolism (PE) in the USA has been estimated at between 300 000 and 650 000 symptomatic events per year.1-3 This ranks venous thromboembolism as the third most common cardiovascular disorder after coronary artery disease and stroke.4 Reported mortality rates for PE have varied from 2% to 25% with the net result in the USA being between 50 000 and 200 000 deaths per year.5-7 However, this number may be an underestimate of the actual morbidity and mortality resulting from PE. Routine necropsy studies have found grossly identifiable clot in up to 30% of cases and microscopic evidence of recent or old thromboemboli in over 50%.8 9 Other studies have shown the diagnosis of acute pulmonary embolism to be unsuspected in 70–80% of patients in whom it was the principal cause of death.10 11 How accurately these data reflect the current position is unclear since modern diagnostic algorithms and approaches to treatment will undoubtedly alter these figures. For many patients who survive acute PE the natural history is one of total …