The incidence of venous thromboembolic disease after hospitalization for elective total hip arthroplasty (THA) was evaluated in a prospective pilot study of 42 patients. Before discharge from the hospital, all patients were free of deep venous thrombosis (DVT) (bilateral lower extremity ascending venography, 38 patients; duplex ultrasonography, two patients; or a combination of both, two patients). After discharge from the hospital, each patient had bilateral duplex ultrasonography and clinical evaluation monthly for three months. Venography was performed when the noninvasive test suggested the presence of DVT. Four (10.5%) of 38 completed patients (95% confidence interval, 4.4-24.8%) developed proximal DVT after hospitalization. Two episodes occurred during the first month after discharge and two during the second month. Three of the four episodes involved the surgically treated extremity. This pilot experience suggests that a significant risk of DVT continues for at least two months after THA. This observation adds support for the emerging clinical trend to continue DVT prophylaxis for at least two months after hospitalization. Further study regarding the incidence of late DVT and its effective prophylaxis seems warranted.