Between 1970 and 1984 the diagnosis of acute, massive lung embolism was made 30 times in our department. In 29 patients the clinical diagnosis was correct and a Trendelenburg operation under extra-corporeal circulation was performed. In 18 cases there was an operation in the immediate preoperative course. In 1 case there was a combination of operation and the use of contraceptives. 3 cases were immobilized by a plaster of Paris cast. In 4 cases the use of oral contraceptives and in 3 patients the history of chronic recurrent lung embolism were evident. The mean immobilisation time was 15 days. In 24 cases the diagnosis was made only on the base of the clinical anamnesis, and examination, E.C.G. and chest radiography. In 4 cases angiography and in 1 patient the scintigraphy confirmed the diagnosis. Preoperatively 28 patients were in severe shock. One patient was operated electively. 14 patients needed external cardiac massage. In all cases clots were found in the left pulmonary artery, 28 in the right pulmonary artery, in 3 cases clots in the right atrium, 3 in the right ventricle and three in the inferior caval vein. Nine De Weese caval vein clips were inserted and one Mobin-Uddin filter. Postoperatively 18 patients were alive and well without sequelae. Two patients developed a cerebro-vascular accident (CVA) with one complete recovery. Ten patients died. Postoperative treatment consisted of I.V. heparin administration immediately after surgery and 6 months of oral anticoagulants. Except for chronic recurrent lung embolism the pulmonary function tests were excellent postoperatively without recurrence of the disease.