One hundred consecutive inpatients with clinically suspected deep venous thrombosis (DVT) were examined by US; the last 19 cases were studied also by means of color-Doppler US. In order to evaluate the method reliability, US results were compared with those obtained with contrast venography, which was performed on all patients. The studied region included the femoro-popliteal vein, while no attempt was made to image the calf veins, which are difficult to evaluate with US. In our series, venographic results were in substantial agreement with US findings, with 99% and 100% sensitivity and specificity, respectively. Diagnosis was based only on noncompressibility of the thrombotic vein, despite the absence of visible clots; pulsed Doppler information supported diagnosis by evaluating blood flow. Further diagnostic progress was provided by color-Doppler US, which allows flow lumen to be defined in color. US also allowed the detection of the conditions mimicking DVT, such as muscular ruptures, hematomas, popliteal cysts, or compressive tumors. In conclusion, US and color-Doppler US prove to be valid alternatives to contrast venography in the diagnosis of proximal DVT of the lower limbs.