In 54 patients with suspected deep vein thrombosis in the lower extremity, B-scan ultrasonography was compared with contrast venography for diagnostic accuracy. In the area of the common femoral/popliteal vein ultrasonography was correct in 53 patients, giving an accuracy of 98% (53/54). There were no false-negative studies, which gives a sensitivity of 100% (21/21). There was one false-positive study for a specificity of 97% (32/33). The technique is inexpensive and produces no discomfort to the patient. It is quite obvious that even small hospitals have the equipment and the competent staff to carry out this examination. We claim that B-scan ultrasonography is a certain, non-invasive method of demonstrating deep vein thrombosis in the common femoral/popliteal vein area.