The prevalence of internal carotid artery stenosis was studied with continuous wave Doppler and Duplex scanning in 526 subjects aged 45-84 years of age. They were devoid of any cerebrovascular symptoms or signs and were not referred to us because of risk factors or manifestations of atherosclerosis. The prevalence of stenosis, whatever the grade, was low in both sexes aged under 65 years: 2.4% in males aged 55-64 years. It increased sharply with age, reaching 30.3% for stenosis of less than 50% and 6.1% for stenosis of greater than 50% in males aged 75-84 years. The prevalence of minimal lesion (plaque with less than 15% diameter reduction) was high: 32.1% in males aged 45-54 years and 48.5% in the 75- to 84-year age range.