The enhanced capability of making a reasonably certain diagnosis of acute pulmonary embolism, which has resulted from the availability of pulmonary perfusion scans and pulmonary angiography, has been accompanied by an evolution of numerous prophylactic and therapeutic measures. Additionally, noninvasive diagnostic tests, including the physical examination, have been reevaluated and refined. The purpose of this article is to outline some of the diagnostic, prophylactic, and therapeutic techniques that have evolved in recent years for the treatment of patients with venous thromboembolism. DEEP-VENOUS THROMBOSIS In assessing the cause of acute pulmonary embolism, it is useful to remember that 80% to 100% of the patients with pulmonary embolism at autopsy have thrombi that originate in the veins of the lower extremities.1 The preponderance of thrombi in the veins of the calves is more than twice that which occurs in the thighs; but the latter remains an important source of thromboemboli.2