Subclinical atherosclerosis can be demonstrated by measuring the intima-media thickness (IMT) of the carotid arteries by high-resolution B-mode ultrasonography (US). Endothelial injury appears a key event in the atherogenesis. Endothelial cell activation and/or injury are the characteristic features of Behçet's disease (BD). In this study, we investigated morphologic evidence of subclinical atherosclerosis in the BD patients by using high-resolution B-mode US. Thirty-four patients with BD without arterial involvement (male/female 21/13; mean age 34.6+/-8.5 years) were individually matched to control subjects on the basis of age (within 2 years) and sex. Subjects with diabetes mellitus, hypertension, evidence of myocardial infarction or cerebrovascular disease, and patients on long-term steroids (i.e., >6 months) were excluded from the study. Mean IMT values of the right carotid arteries were 0.81+/-0.17 mm for patients with BD, and 0.54+/-0.13 mm for healthy controls (P<0.001). Mean IMT values of the left carotid arteries were 0.82+/-0.16 mm for patients with BD, and 0.55+/-0.12 mm for healthy controls (P<0.001). The overall prevalence of carotid atherosclerotic plaques was higher among the patients than the controls [prevalence of plaques were 17.6% (6/34) in BD patients and 0% in healthy controls, P<0.05]. In conclusion, our data indicate morphologic evidence of subclinical atherosclerosis in patients with BD.