Between July 1985 and September 1987, 25 patients underwent 26 carotid endarterectomies based on an abnormal duplex scan (B-mode ultrasonography and pulsed-Doppler sound spectral analysis) indicative of severe stenosis or ulceration. Arteriography was not performed because of severe unstable angina requiring coronary artery bypass grafting (23 patients) or patient preference (two). Twelve patients were symptomatic, and 13 were asymptomatic but had severe (greater than or equal to 75%) bilateral or unilateral carotid artery stenosis. Operative and pathological analyses confirmed the duplex-scan findings in all 25 cases. All 25 patients survived the operation. One patient had a transient ipsilateral neurological deficit, and one had a permanent contralateral neurological deficit. Five patients died of ventricular arrhythmias within 30 days of operation. Duplex scanning is an accurate method for determining the presence of clinically and hemodynamically significant carotid arterial occlusive disease. Duplex scanning also serves as an alternative method for evaluating patients for whom carotid arteriography may be associated with significant risk.