Venous thromboembolism (VTE) prophylaxis is indicated while in the hospital after major surgery. There is evidence that the prevalence of asymptomatic deep-vein thrombosis, detected by routine venography after major orthopedic surgery, is lower at hospital discharge in patients who have received 10 days rather than 5 days of prophylaxis. This observation supports the current American College of Chest Physicians (ACCP) recommendation for a minimum of 7 to 10 days of prophylaxis after hip and knee replacement, even if patients are discharged from the hospital within 7 days of surgery. As risk of VTE persists for up to 3 months after surgery, patients at high risk for postoperative VTE may benefit from extended prophylaxis (eg, an additional 3 weeks after the first 7 to 10 days). Extended prophylaxis with low-molecular-weight heparin (LMWH) reduces the frequency of postdischarge VTE by approximately two thirds after hip replacement; however, the resultant absolute reduction in the frequency of fatal pulmonary embolism is small (ie, estimated at 1 per 2,500 patients). Indirect evidence suggests that, compared with LMWH, efficacy of extended prophylaxis after hip replacement is greater with fondaparinux, similar with warfarin, and less with aspirin. Extended prophylaxis is expected to be of less benefit after knee than after hip replacement. In keeping with current ACCP recommendations, at a minimum, extended prophylaxis should be used after major orthopedic surgery in patients who have additional risk factors for VTE (eg, previous VTE, cancer). If anticoagulant drug therapy is stopped after 7 to 10 days, an additional month of prophylaxis with aspirin should be considered.