Chronic recurrent pulmonary emboli may lead, in rare cases, to progressive pulmonary arterial hypertension which cannot be treated medically. These patients may be helped by bilateral pulmonary thrombendarterectomy. The value of spiral CT in the diagnosis of this condition was demonstrated in 31 patients. In 12 patients, thrombi could be shown to be the cause of the pulmonary arterial hypertension. Indirect criteria were vascular occlusions, changes in calibre and mural irregularities which were shown in varying degrees in all patients. In 22 of 31 patients there was non-homogeneity of perfusion with greater opacification of the perfused lung parenchyma. In 11 patients scars related to pleural surfaces were seen. Typical changes of right heart insufficiency (cardiomegaly, widened central pulmonary arteries) were shown in all patients by CT.