Background. The incidence of pulmonary hypertension resulting from chronic thrombotic occlusion of the pulmonary arteries is significantly underestimated. Although medical therapy for the condition is supportive only, surgical therapy is curative. Our pulmonary endarterectomy program was begun in 1970, and 188 patients were operated on in the subsequent 20 years. With the increased recognition of the disease and the success of operative therapy, however, more than 1,400 operations have been done since 1990 at our center. Methods. The safety and efficacy of the operation was assessed with changes made through increased experience. We examined in detail the results of our last 500 consecutive patients. Results. Median sternotomy, cardiopulmonary bypass, profound hypothermia, and circulatory arrest were found to be essential to the success of the operation. All occluding material could be removed at operation. We currently believe that there is no degree of embolic occlusion within the pulmonary vascular tree that is inaccessible and no degree of right ventricular impairment or any level of pulmonary vascular resistance that is inoperable. With shorter cardiac arrest periods and the use of a cooling jacket to the head, cerebral impairment has been eliminated. The pulmonary artery pressures and pulmonary vascular resistance in a recent cohort of 500 patients is examined. The mortality rate for the operation has been reduced steadily, and was 22 of the last 500 patients operated on (4.4%). Conclusions. The operation is considered curative and therefore greatly superior to transplantation for this condition. Current techniques of operation make the procedure relatively safe. © 2003 by The Society of Thoracic Surgeons.