The effects of continuous epidural anesthesia and of general anesthesia on the incidence of thromboembolism following total hip replacement were studied. Sixty patients were randomly allotted to one of two groups receiving either epidural or general anesthesia. Epidural anesthesia (N = 30) consisted of 0.5% bupivacaine with epinephrine intraoperatively; for pain relief in the postoperative period (24 h), 0.25% bupivacaine with epinephrine was given every 3 h. General anesthesia (N = 30) consisted of controlled ventilation with N2O-O2 and intravenous fentanyl and pancuronium bromide; postoperatively, narcotic analgesics were given intramuscularly on demand for pain relief. Significantly lower frequencies were found following epidural anesthesia than after general anesthesia in deep venous thrombosis involving the popliteal and femoral veins (13% and 67%, respectively), deep venous thrombosis involving both calf and thigh veins (40% and 77%), and pulmonary embolism (10% and 33%). Possible explanations for these differences include increased circulation in the lower extremities, less tendency for intravascular clotting to occur, and more efficient fibrinolysis in association with continuous epidural anesthesia. The decrease in blood loss associated with epidural anesthesia with lower transfusion requirements also might play a role. Epidural analgesia prolonged into the postoperative period, in addition to other appropriate thromboprophylactic measures, should be of value in patients undergoing operations associated with a high risk of thromboembolic complications.