To assess vein compressibility as a simple ultrasound (US) technique to determine the presence of venous thrombi, 51 patients undergoing contrast material venography of the lower extremity because of a clinical suspicion of deep venous thrombosis (DVT) also underwent high-resolution US evaluation of the veins. DVT was diagnosed on 28 venograms. In 25 patients US studies demonstrated non-compressibility of the veins, indicating the presence of clot. In 23 patients with normal venograms, US examinations demonstrated total compressibility of the veins, indicating the absence of DVT. Clots below the knee were not depicted by US. In this study US had a sensitivity of 89% and a specificity of 100%.