This study evaluated the role of duplex scanning in the management of patients with normal or minimally diseases carotid arteries. Carotid duplex scans were interpreted according to previously established criteria and considered normal when pulsed Doppler spectral waveforms showed laminar flow or only minor flow disturbances. Normal flow patterns were noted by duplex scanning in 100 carotid bifurcations of 72 patients who also underwent carotid arteriography. Neurologic symptoms (amaurosis fugax, transient ischemic attack, or stroke) were present in relation to 23 arteries and absent in relation to 77 arteries. On the 23 symptomatic sides arteriography was interpreted as normal in eight, 1% to 15% stenosis in 14, and 16% to 40% stenosis in one. For the 77 asymptomatic sides, arteriography showed normal vessels in 15, 1% to 15% stenosis in 43, and 16% to 40% stenosis in 19. One symptomatic patient was treated by carotid endarterectomy for an irregular 1% to 15% stenosis. None of the asymptomatic lesions were in the range of 80% to 99% stenosis, which would justify endarterectomy for asymptomatic disease. Clinical follow-up for a mean interval of 28 months on 20 of the 22 symptomatic patients not undergoing surgery revealed no strokes and transient recurrent symptoms in two patients. Assuming that the single operation in this study was indicated, duplex scanning correctly identified lesions not requiring carotid endarterectomy in 96% (22/23) of the symptomatic patients. A normal duplex scan also predicted a benign clinical outcome without operation. Duplex scanning can reliably exclude surgically treatable carotid bifurcation lesions in asymptomatic patients, and endarterectomy is rarely indicated in symptomatic patients with normal duplex scan results. This study supports a nonoperative therapeutic approach for most patients with neurologic symptoms and a normal carotid duplex scan on the appropriate side.