OBJECTIVE To determine the utility of duplex ultrasound scanning of the renal arteries in identifying patients with renal artery stenosis of 60% or more and in excluding patients with either normal renal arteries or renal artery stenosis of less than 60%. METHODS A prospective, blinded study. METHODS Large tertiary referral center. METHODS 102 consecutive patients (44 men and 58 women with a mean age [+@- SD] of 63.3 +/- 13.4 years) who had both duplex ultrasound scanning of the renal arteries and renal arteriography. All patients who were studied had hypertension that was difficult to control, unexplained azotemia, or associated peripheral vascular disease (alone or in combination), giving them a high pretest likelihood of renovascular disease. METHODS Peak systolic and end diastolic velocities, renal-aortic ratios, resistive index, and kidney sizes. RESULTS Sixty-two of 63 arteries with stenosis of less than 60% using arteriography were correctly identified by duplex ultrasound scanning. Thirty-one of 32 arteries with 60% to 79% stenosis using arteriography were correctly identified as having 60% to 99% stenosis on duplex ultrasound, whereas 67 of 69 arteries with 80% to 99% stenosis on arteriography were correctly identified as having 60% to 99% stenosis on ultrasound. Twenty-two of 23 arteries with total occlusion on arteriography were correctly identified by duplex ultrasound. The overall sensitivity of duplex ultrasound compared with arteriography was 0.98, the specificity was 0.98, the positive predictive value was 0.99, and the negative predictive value was 0.97. CONCLUSIONS Duplex ultrasound scanning of the renal arteries is an ideal screening test because it is noninvasive and can predict the presence or absence of renal artery stenosis with a high degree of accuracy.