A 57-year-old man with dyspnea and dry cough exhibited pulmonary embolism. Pulmonary arteriography demonstrated absent perfusion of the left main and the right upper and middle lobe pulmonary arteries. A diagnosis of chronic pulmonary thromboembolism was assumed and surgical thromboendarterectomy was attempted under standard cardiopulmonary bypass. At operation, a tumor had invaded far into both the right and left pulmonary arteries and radical resection was impossible. The final pathological diagnosis was primary leiomyosarcoma of the pulmonary artery. The patient refused any adjuvant therapy and died 63 days after the surgery. The clinical presentation of this case was similar to that of pulmonary thromboembolism and its diagnosis and treatment were very difficult.