Since 1986, American College of Chest Physicians (ACCP) has been regularly releasing guidelines for antithrombotic therapy for prevention and treatment of thrombosis. The sixth ACCP consensus 2001 conference has recommended successful prevention strategies in surgical patients. A few Japanese prospective studies disclosed that the incidence of deep vein thrombosis(DVT) after general surgery in Japan is about half in western countries. On the other hand, it is reported that the incidence of DVT after total hip replacement and total knee replacement in Japan is almost as same as in western countries. Since there is still little data available for the incidence of postoperative DVT and pulmonary thromboembolism in Japan, it is necessary to organize some prospective multicenter surveys for them.