In the contemporary clinical setting, a diagnosis of deep vein thrombosis can be established using ultrasound. While different ultrasound modalities, including direct B-mode venous imaging, Doppler, and vein compression, have been employed to diagnose clot, it is the compression technique that has been established as the dominant method. In venographically controlled series, compression ultrasound has demonstrated a 93% sensitivity and 99% specificity for clot detection. These remarkable results have been achieved without the evaluation of calf veins. Recent improvements in instrumentation have permitted the direct visualization of calf veins, and it would seem likely that this will result in even better sensitivity for clot detection.