Cancer patients are prone to both thrombotic and tumor pulmonary embolism (PE). To identify similarities and differences in their clinical features, we reviewed all autopsies from 1978 to 1982 at Brigham and Women's Hospital and the Dana Farber Cancer Institute. Of 73 patients with solid malignant tumors and PE, 56 had major thrombotic PE and 17 had major tumor embolism to the lungs. Of the 56 with cancer and thrombotic PE, 25 (45%) had the correct diagnosis suspected antemortem. By contrast, only 1 of 17 (6%) patients with tumor embolism was diagnosed correctly antemortem (p = 0.005). Most presenting symptoms, signs, laboratory values, and associated conditions were not markedly different in patients with thrombotic PE and tumor embolism. These findings indicate that tumor PE is more difficult to diagnose clinically and may be misdiagnosed as thrombotic PE. Finally, these data suggest that in all cancer patients, the presence of both thrombotic and tumor PE should be considered because of similarities in their clinical features.