A consecutive series of 369 asymptomatic patients with a carotid bruit was prospectively followed with Ocular Pneumoplethysmography (OPG). The aim of the study was to identify those patients most prone to cerebrovascular ischemia and/or progression of obstructive carotid disease. During follow-up 13 patients developed a stroke of which six were fatal (two thrombo-embolic and four haemorrhagic strokes). TIA's occurred in 15 patients, including eight patients with amaurosis fugax. TIA's occurred more frequently on the side of a haemodynamically significant stenosis (9% = 9/95) than on the side of a normal, OPG (2% = 6/274). There was no difference in the strokelocated side. The occurrence of symptoms and/or signs of cerebrovascular disease was 4% at two years and 10% at five years. The left hemisphere was affected twice as often as the right. The development of a haemodynamically significant carotid stenosis, according to OPG, was equal for the right and the left carotid arteries, being 18% at two years and 56% after 5 years of follow-up. The major risk factors for progression of obstructive disease were systolic blood pressure above 160 mmHg independent of age, diabetes mellitus and the presence of ischaemic heart and peripheral arterial obstructive disease. This study supports the contention that in a group of patients with an asymptomatic carotid bruit, a group of patients at risk from cerebrovascular accidents can be filtered out by a simple non-invasive test in combination with a complete physical examination.