The association between plasma C-reactive protein (CRP), a marker of systemic inflammation, and the metabolic syndrome is well recognized. However, information is scant regarding the component of metabolic syndrome that is critical in modulating CRP levels in younger adults. This aspect was examined in a biracial (black-white) community-based sample of 1083 younger adults (mean age, 36.1 years; 71% white, 45% male) enrolled in the Bogalusa Heart Study. Plasma CRP along with metabolic syndrome variables were measured. CRP levels showed a significant race (black>white, P=.01) and sex (female>male, P=.0001) differences, and related to measures of obesity (body mass index [BMI], waist circumference, and sagittal diameter), blood pressure (systolic, diastolic, and mean arterial blood pressure), lipoproteins (low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, total cholesterol-high-density lipoprotein cholesterol ratio), glucose homeostasis (insulin, glucose, homeostasis model assessment of insulin resistance), and uric acid, after adjusting for age, race, sex, and cigarette smoking. Furthermore, CRP levels increased with increasing number of metabolic syndrome risk factors, as defined by the National Cholesterol Education Program Adult Treatment Panel III, regardless of race and sex (P for trend<0001). In multivariate analysis, using 3 separate models for different obesity measures, obesity was the major contributor to the explained variance in each model with BMI, waist, and sagittal diameter contributing 17.0%, 13.4%, and 17.1% of the variance, respectively. In contrast, homeostasis model assessment of insulin resistance contributed 1.2%, 0.3%, and 0% to the explained variance in the models with BMI, waist, and sagittal diameter, respectively. In conclusion, CRP levels differ among race and sex groups and correlate to metabolic syndrome variables in younger adults. In addition, these findings strongly suggest that although obesity and insulin resistance are the main underlying features of the metabolic syndrome, the former appears to be the major mediator of CRP levels, which has important health implications.