High-resolution real-time ultrasonography was performed in 11 patients with clinically suspected deep venous thrombosis (DVT) of the lower extremity. Contrast venography was performed in all patients within 24 hours of sonographic examination. The common femoral vein at the groin and the popliteal vein in the popliteal fossa were evaluated for presence or absence of intraluminal soft-tissue mass (thrombi), compressibility of the veins, and response to performance of the Valsalva maneuver. Of the 11 patients, six were shown to have DVT by contrast venography. In all six cases there was complete agreement between sonography and contrast venography as to the presence or absence of thrombi in the common femoral vein or the popliteal vein.