The results of previous studies have suggested that significant stenosis of the carotid artery occurs in less than 6 per cent of asymptomatic patients. However, some populations studied were not representative of those seen by most vascular surgeons. Accordingly, we examined two cohorts of patients at the Veterans Administration Medical Center using Duplex scanning. There were 153 volunteers in group 1, all more than 50 years of age, who were being treated at our outpatient department for nonvascular problems. There were 116 patients of similar age in group 2 but who were known to have significant arterial occlusive disease of the lower extremity. The majority of patients were men with a mean age of 64.4 years. Risk factors in the total population included hypertension, diabetes mellitus, coronary arterial disease, peripheral vascular disease and smoking. Over-all, significant (greater than 50 per cent diameter) stenosis of the carotid artery was discovered in 25 of 269 patients. The prevalence for those in group 1 was 6.5 per cent versus 12.9 per cent for those in group 2 (p = 0.058). The prevalence in patients with cardiac disease was 15.2 per cent compared with 6.8 per cent in those without cardiac disease (p = 0.032). Smoking was associated with a 10.6 per cent rate of significant disease compared with a 2.3 per cent rate in nonsmokers (p = 0.065). Hypertension and diabetes were not significant risk factors. Significant stenosis of the carotid artery was found in seven of 40 patients in whom coronary arterial disease, peripheral vascular disease and smoking were all present.(ABSTRACT TRUNCATED AT 250 WORDS)