Difficulties persist in the accurate clinical diagnosis of major pulmonary embolism despite the availability of lung scans and pulmonary angiography. To evaluate factors associated with the correct antemortem diagnosis of pulmonary embolism, we reviewed all 1,455 autopsy reports at the Peter Bent Brigham Hospital from 1973 to 1977. Of 54 patients identified with anatomically major pulmonary embolism at autopsy, 16 (30 percent) had correct antemortem diagnosis. Accuracy was far greater in postoperative patients (64 percent) (p = 0.02) and in patients with autopsy-proved venous thrombosis (55 percent) (p = 0.005). Lung scanning (82 percent) (p = 0.0002) and pulmonary angiography (80 percent) (p = 0.05) during the 10 days prior to death were also associated with an increased tendency to correct clinical diagnosis of pulmonary embolism. In contrast, among 21 patients with autopsy-proved major pulmonary embolism who also had pneumonia, no pulmonary embolism was diagnosed before death (p = 0.0001). Furthermore, among patients 70 years of age or older, only 10 percent with pulmonary embolism at postmortem examination had a correct diagnosis prior to death (p = 0.02). In patients with pneumonia or in elderly patients, an increased awareness of the possibility of pulmonary embolism and more frequent use of lung scanning and pulmonary angiography may increase the accurate clinical diagnosis of pulmonary embolism.