Continuous-wave (CW) Doppler sonography has proved to be a reliable tool both to detect subclavian stenosis or occlusion and to detect reversal of blood flow in the vertebral artery. This method is entirely atraumatic and in contrast to angiography allows investigation of asymptomatic patients and provides more representative data for epidemiological studies. The incidence of subclavian stenosis or occlusion was 1.15% among the 23,500 patients examined in our department between 1978 and 1985. Of the 272 patients with unilateral or bilateral subclavian stenosis or occlusion, 54% were asymptomatic with no subjective complaints and were normal upon neurological examination; 29% reported vertebrobasilar transient ischaemic attacks (TIAs), with or without concomitant TIAs or infarction in the vascular territory of the carotid arteries; and 17% complained of symptoms exclusively referring to the region of carotid blood supply. Reversal of blood flow in the ipsilateral vertebral artery was detected in 152 patients (56%). The incidence of neurological symptoms within this group was double that found in patients without steal. None of the patients suffered from permanent vertebrobasilar damage. In most cases, subclavian artery disease was due to atherosclerosis. For 13 patients an inflammatory, iatrogenic, traumatic, or congenital aetiology could be assumed. The marked preponderance of left-sided subclavian stenosis or occlusion, reported by others, could be confirmed among our patients, but was less pronounced for tight stenoses than for occlusions. Mild-to-moderate subclavian stenoses were about equally distributed on each side.