873 patients who had undergone elective total hip or knee replacement were randomized to receive 3 weeks of treatment with either enoxaparin or a placebo. This treatment was after subcutaneous injections of enoxaparin administered 7-10 days postoperatively to all patients. The primary outcome was the prevalence of venous thromboembolism or symptomatic pulmonary embolism during the treatment phase. Additional enoxaparin significantly reduced the prevalence of venous thromboembolism in comparison with placebo. This effect was not seen in patients with knee replacement.