We determined the prevalence of the metabolic syndrome (MS) with the criteria recommended by the National Cholesterol and Education Program, Adult Treatment Panel III report and estimated the magnitude of cross-sectional associations between the MS, coronary heart disease (CHD), and atherosclerosis in 14,502 black and white middle-age patients in the Atherosclerosis Risk in Communities Study. CHD was ascertained by standardized procedures and subclinical atherosclerosis was determined by measuring carotid intimal medial wall thickness using B-mode ultrasonography. The prevalence of MS was 30%, with substantial variation across race and gender subgroups. Among women but not among men, MS was significantly associated with increasing low-density lipoprotein cholesterol. CHD prevalence was 7.4% among those with the MS compared with 3.6% in comparison subjects (p <0.0001). After adjustment for established risk factors, subjects who had MS were 2 times more likely to have prevalent CHD than were those who did not have the syndrome. Among individuals free of CHD and stroke, after adjustment for age, gender, and race/center, the average intimal-medial wall thickness of carotid arteries was greater among those with versus those without MS (747 vs 704 mum, p <0.0001). Thus, MS was significantly associated with the presence of CHD and carotid intimal medial wall thickness. Identification of patients who have MS may provide opportunities to initiate CHD prevention strategies.