Venous thromboses of the pelvic veins and the veins of the lower limbs were found in 40% of the post mortems carried out on 1350 adults during 1974. The thromboses were bilaterally located in the calf veins in the vast majority of cases. The predominating underlying diseases of patients with thrombosis were malignant neoplasia or cardiovascular diseases. 319 cases (23.5%) showed massive pulmonary embolism. The pulmonary embolism had taken a fulminating fatal course in 7.8% of cases. Thromboses of the lower limb veins seem to have a higher tendency to become mobilized to cause fatal pulmonary embolism than thromboses occurring in other sites. A significantly higher incidence of venous thrombosis, as well as of pulmonary embolism, was found in higher age groups and in female patients; the prognosis is, moreover, grave in these cases. A significant increase in the incidence of venous thromboses and pulmonary embolism-especially those with a rapidly fatal course-has been registered over the past years as compared with previous investigations.