Background: Venous thromboembolic disease in the form of deep venous thrombosis and pulmonary embolism is a major risk after a total hip arthroplasty. Enoxaparin, a low-molecular-weight heparin, has been shown to reduce the prevalence of deep venous thrombosis after total hip arthroplasty. Warfarin, an orally administered anticoagulant, has been used historically to reduce the risk of deep venous thrombosis after total hip arthroplasty. Methods: We compared enoxaparin and adjusteddose warfarin with respect to their safety and their efficacy in the prevention of clinically important venous thromboembolic disease, defined as distal or proximal deep venous thrombosis or pulmonary embolism, or both, during hospitalization after total hip arthroplasty. We also evaluated the prevalence of complications and mortality from venous thromboembolic disease within three months after discharge. Results: Three thousand and eleven patients at 156 centers were randomly assigned to prophylactic treatment with injection of enoxaparin or oral administration of adjusted-dose warfarin during hospitalization. During the study, fifty-five (3.6 percent) of the 1516 patients who were managed with enoxaparin and fifty-six (3.7 percent) of the 1495 patients who were managed with warfarin had venous thromboembolic gene, Oregon 97401.