Few studies have reported on the relationship between metabolic syndrome (MetS) and carotid artery structure. The objective of this study was to examine the relationship between MetS and carotid artery parameters such as the common carotid artery intima-media thickness (CCA-IMT), plaques, and the diameter of the common carotid artery (CCAd). The study population consisted of 1.730 community-dwelling Koreans aged 50 years and older without hypertension, diabetes mellitus or dyslipidemia. MetS was defined according to the modified National Cholesterol Education Program's Adult Treatment Panel III criteria. The risk for abnormal CCA-IMT (>or=1.00 mm) was significant in women with MetS (odds ratio (OR) 2.22; 95% confidence interval (CI) 1.14-4.31), but not in men with MetS (OR 1.06; 95%CI 0.39-2.91). No significant relationship between MetS and carotid plaques was observed in either sex. The relationship between MetS and high CCAd (highest quintile) was significant in both men (OR 2.19; 95%CI 1.38-3.49) and women (OR 2.02; 95%CI 1.39-2.94). MetS independently correlates with carotid atherosclerosis and carotid enlargement. The effect of MetS on carotid atherosclerosis is more pronounced in women than in men.