OBJECTIVE: The aim of this study was to describe the association of the metabolic syndrome with demographic characteristics and to identify modifiable risk factors for development of the metabolic syndrome. RESEARCH DESIGN AND METHODS: Men and women (55%) aged 18-30 years from the Coronary Artery Risk Development in Young Adults (CARDIA) study without the metabolic syndrome at baseline (n = 4,192, 49% black) were followed-up from 1985 to 2001. Incident metabolic syndrome, defined according to the National Cholesterol Education Program Adult Treatment Panel III criteria, was ascertained 7, 10, and 15 years after baseline. Risk factors were measured via clinical examination and standardized questionnaires. RESULTS: The age-adjusted rate of metabolic syndrome was 10 per 1,000 person-years (n = 575). Metabolic syndrome risk increased with age and was higher among black participants and those with less than a high school education. Higher baseline BMI, no alcohol intake (versus one to three drinks per day), higher intake of dietary carbohydrates, and lower intake of crude fiber were each associated with an increased risk for the metabolic syndrome (relative risk [RR] ranging from 1.3 to 1.9), and physical activity was protective (RR 0.84 [95% CI 0.76-0.92]). In models adjusting simultaneously for all factors, black participants and women were less likely to develop metabolic syndrome. Risk for metabolic syndrome increased 23% (20-27%) per 4.5 kg (10 lb) of weight gained, whereas regular physical activity over time versus low activity was protective (RR 0.49 [0.34-0.70]). CONCLUSIONS: BMI and weight gain are important risk factors for the metabolic syndrome. Regular physical activity may counter this risk.