Patients (102) presenting at the outpatient departments of 2 Boston [USA] teaching hospitals underwent clinical examination and venography. History, physical examination and presence of risk factors were unreliable in the diagnosis of deep venous thrombosis. Of the patients with deep venous thrombosis, 72% had a proximal extension of the thrombus to the femoral vein or higher. The out-patient with deep venous thrombosis appears to differ from the more frequently studied inpatient in the time of diagnosis and its anatomic extent. The high incidence of false-positive clinical examination results has important cost-benefit implications.