Sixty-seven patients with pulmonary embolic disease (diagnosed clinically and with perfusion lung scans) were studied. In 48 of them, the scans were interpreted as positive for pulmonary emboli and in 19, as questionable. All 67 patients underwent pulmonary arteriography. The pulmonary arteriogram showed no evidence of pulmonary embolus in 11 of the 48 patients with positive findings on lung scan and no evidence in 12 of the 19 patients with questionable lung scan. Because of the high false-positive rate of the perfusion lung scan, we strongly recommend angiographic confirmation of pulmonary embolism when interruption of inferior vena cava is contemplated for the prevention of recurrence of pulmonary embolism.