A prospective study of 222 consecutive autopsies of cancer cases was undertaken to investigate whether carcinomatous lymphangitis and pure arterial tumor embolism of the lungs are different clinicopathological entities. The lungs were removed as a block and 15 sections (three from each lobe) were analyzed. A protocol containing clinical (ie, dyspnea, cyanosis, right ventricular failure, engorgement of jugular veins, and peripheral edema as main cause of death) and morphological (ie, right ventricle thickness and dilatation, vascular sclerosis, pulmonary infarct) data were carefully recorded in each case. Arterial tumor embolism was detected in 19 cases (8.5%) and carcinomatous lymphangitis in 44 cases (19.8%). We found no differences in relation to signs and symptoms of arterial tumor embolism and carcinomatous lymphangitis, but respiratory distress as the main cause of death was significantly more frequent in the cases with arterial involvement by tumor emboli. Morphologically, however, right ventricular hypertrophy-dilatation, histological signs of pulmonary hypertension, and hemorrhagic infarcts were more prevalent in the cases with arterial tumor embolism. This study permits us to conclude that although arterial tumor embolism and carcinomatous lymphangitis are clinically similar diseases, they are morphologically different entities. Our results suggest that the most probable pathogenesis of pulmonary endarteritis and subsequent pulmonary hypertension is the injury to the vascular endothelium caused by the arrest of tumor emboli.