This is a prospective study of aspirin prophylaxis and thromboembolism surveillance in 159 patients having total hip arthroplasty by one surgeon at one institution. All patients had preoperative venous Doppler examination of the lower extremities and a ventilation-perfusion lung scan. Aspirin (650 mg) was given the night prior to surgery and continued at that dose twice per day. Venous Doppler examination was performed 10-14 days after operation. Asymptomatic pulmonary embolism was treated with oral anticoagulation only. There was a 12.6% incidence of pulmonary embolism, but only 1.9% of all patients developed a symptomatic pulmonary embolus. No patient had a fatal pulmonary embolus. No patient had a clinically evident deep vein thrombosis, and venous Doppler examination detected only nine patients with deep vein thrombosis (5.7%). The venous Doppler examination could not predict which patients would develop a pulmonary embolism. The authors could not determine a group of patients at high risk for the development of pulmonary embolism. There was no correlation between well-established "risk factors" and the development of pulmonary embolism. There was no correlation between the use of cemented or uncemented components and the development of pulmonary embolism. There were few complications of this prophylactic regimen of aspirin and surveillance. The authors believe this may be an acceptable prophylactic regimen for patients having total hip arthroplasty. However, the value of venous Doppler examination in the detection of deep vein thrombosis following total hip arthroplasty is uncertain.