The risk of stroke in patients with asymptomatic carotid disease appears to be related to the presence of a high-grade stenosis. To determine the prevalence of such lesions, duplex scanning was performed on 348 unselected volunteers without symptoms who attended hospital-sponsored health fairs. There were 209 women and 139 men whose ages ranged from 24 to 91 years. Risk factors included hypertension (37%), diabetes (8%), and smoking (23%). One hundred seven subjects (31%) had evidence of extracranial carotid artery disease, 13 (4%) with greater than 50% stenosis, and three (1%) with greater than 80% stenosis of the internal carotid artery. Bilateral disease was present in 50 patients. Disease prevalence and severity were significantly correlated with age (p less than 0.001) and hypertension (p less than 0.01) but not with diabetes or smoking. The incidence of disease was similar in men and women. Although carotid plaques are common in people older than 50 years of age who do not have symptoms, the prevalence of high-grade stenosis--even in the elderly hypertension population--is low, casting doubt on the cost-effectiveness of generalized screening.