349 patients undergoing knee arthroplasty were randomized to receive thromboprophylaxis with enoxaparin or warfarin postoperatively. Patients were assessed for venous thromboembolism defined as deep vein thrombosis and pulmonary vein thrombosis. Enoxaparin was significantly more effective than adjusted‐dose warfarin in reducing the occurrence of asymptomatic venous thromboembolism, including proximal deep‐vein thrombosis, in patients undergoing total knee arthroplasty. Overall hemorrhagic complications occurred at a significantly higher rate in the enoxaparin group, but with no significant difference for major events.