The ability of real-time B-mode ultrasound to directly visualize arteries and veins and thereby give anatomic rather than physiologic information is unique among the currently available noninvasive methods of vascular evaluation. The usefulness of this technique for examination of the carotid arteries has been well proven. Little attention, however, has been given to its applicability for deep venous evaluation. Over the past 12 months the veins of 108 upper and 215 lower extremities have been studied with high-resolution real-time ultrasound. The technique and interpretive criteria are presented. Thirty extremities underwent confirmatory venography, and in this group the specificity and sensitivity of the ultrasound were 94% and 100%, respectively. In addition, the age of the thrombi detected was accurately predicted in 93% of this group. These preliminary results suggest that real-time B-mode venous ultrasound is an accurate, clinically useful noninvasive technique for the detection of deep venous thrombosis that complements the more widely used physiologic screening tests.