Abstract : We studied all the patients who underwent a total hip arthroplasty during the last six months of 2001. They all had a postoperative venous Doppler echo (possibly repeated) followed by a phlebography in case of clinical doubt. They all received a prophylactic treatment by low molecular weight heparin. Our rate of deep venous thrombosis was 22% (from which 3% are) and of pulmonary emboli was 2,7%. These figures are in keeping with those of large controlled studies. The risk factors identified are age and female gender. We discuss, based on the literature, the significance of lower deep venous thrombosis. We also discuss the best strategy to detect postoperative deep venous thrombosis in order to improve the cost/effectiveness ratio