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Thromboembolic disease continues to pose a significant risk to patients undergoing total joint arthroplasty, but the clinical significance of a deep venous thrombosis (DVT) in the postoperative period remains controversial. This report reviews the outcome of 920 patients undergoing prospective obtained venograms after total hip and total knee surgery. Six hundred two patients also obtained postoperative ventilation perfusion scans (V/Q). All patients received one of the following forms of prophylaxis: aspirin (79%), warfarin (16%), or low-molecular-weight heparin (5%). The results show that 39% were without any clot, 36% had small calf thrombi, 19% had large calf thrombi, 2.5% had popliteal thrombi, and 3.8% had femoral thrombi. Calf thrombi occurred almost 2.5 times more frequently after total knee arthroplasty than total hip arthroplasty (67% versus 27%), yet the incidence of pulmonary embolism (PE) is the same in both groups. Intermediate or high probability V/Q results occurred in 103 patients (15%). There was a positive association between the size of a clot and the likelihood of an intermediate- or high-probability V/Q scan. Thromboembolic events resulted in five symptomatic PE (0.5%) and two deaths (0.2%), one in the hospital on warfarin, and one as an outpatient on aspirin. From these data, the authors conclude that calf thrombi by themselves do not place a patient at risk and are not accurate markers of a patient being at risk. Larger clots have a greater likelihood to embolize, but the size of the clot that is clinically significant is undetermined. A significant chance of a PE after discharge from the hospital warrants some form of continuing prophylaxis in outpatients.