Although the individual components of the metabolic syndrome are clearly associated with increased risk for coronary heart disease (CHD), we wanted to quantify the increased prevalence of CHD among people with metabolic syndrome. The Third National Health and Nutrition Examination Survey (NHANES III) was used to categorize adults over 50 years of age by presence of metabolic syndrome (National Cholesterol Education Program [NCEP] definition) with or without diabetes. Demographic and risk factor information was determined for each group, as well as the proportion of each group meeting specific criteria for metabolic syndrome. The prevalence of CHD for each group was then determined. Metabolic syndrome is very common, with approximately 44% of the U.S. population over 50 years of age meeting the NCEP criteria. In contrast, diabetes without metabolic syndrome is uncommon (13% of those with diabetes). Older Americans over 50 years of age without metabolic syndrome regardless of diabetes status had the lowest CHD prevalence (8.7% without diabetes, 7.5% with diabetes). Compared with those with metabolic syndrome, people with diabetes without metabolic syndrome did not have an increase in CHD prevalence. Those with metabolic syndrome without diabetes had higher CHD prevalence (13.9%), and those with both metabolic syndrome and diabetes had the highest prevalence of CHD (19.2%) compared with those with neither. Metabolic syndrome was a significant univariate predictor of prevalent CHD (OR 2.07, 95% CI 1.66-2.59). However, blood pressure, HDL cholesterol, and diabetes, but not presence of metabolic syndrome, were significant multivariate predictors of prevalent CHD. The prevalence of CHD markedly increased with the presence of metabolic syndrome. Among people with diabetes, the prevalence of metabolic syndrome was very high, and those with diabetes and metabolic syndrome had the highest prevalence of CHD. Among all individuals with diabetes, prevalence of CHD was increased compared with those with metabolic syndrome without diabetes. However, individuals with diabetes without metabolic syndrome had no greater prevalence of CHD compared with those with neither.