BACKGROUND: Consumption of soft drinks has been linked to obesity in children and adolescents, but it is unclear whether it increases metabolic risk in middle-aged individuals. METHODS AND RESULTS: We related the incidence of metabolic syndrome and its components to soft drink consumption in participants in the Framingham Heart Study (6039 person-observations, 3470 in women; mean age 52.9 years) who were free of baseline metabolic syndrome. Metabolic syndrome was defined as the presence of > or = 3 of the following: waist circumference > or = 35 inches (women) or > or = 40 inches (men); fasting blood glucose > or = 100 mg/dL; serum triglycerides > or = 150 mg/dL; blood pressure > or = 135/85 mm Hg; and high-density lipoprotein cholesterol < 40 mg/dL (men) or < 50 mg/dL (women). Multivariable models included adjustments for age, sex, physical activity, smoking, dietary intake of saturated fat, trans fat, fiber, magnesium, total calories, and glycemic index. Cross-sectionally, individuals consuming > or = 1 soft drink per day had a higher prevalence of metabolic syndrome (odds ratio [OR], 1.48; 95% CI, 1.30 to 1.69) than those consuming < 1 drink per day. On follow-up (mean of 4 years), new-onset metabolic syndrome developed in 717 of 4033 participants (17.8%) consuming < 1 drink/day and in 433 of 2006 persons (21.6%) [corrected] consuming > or = 1 soft drink/day [corrected] Consumption of > or = 1 soft drink per day was associated with increased odds of developing metabolic syndrome (OR, 1.44; 95% CI, 1.20 to 1.74), obesity (OR, 1.31; 95% CI, 1.02 to 1.68), increased waist circumference (OR, 1.30; 95% CI, 1.09 to 1.56), impaired fasting glucose (OR, 1.25; 95% CI, 1.05 to 1.48), higher blood pressure (OR, 1.18; 95% CI, 0.96 to 1.44), hypertriglyceridemia (OR, 1.25; 95% CI, 1.04 to 1.51), and low high-density lipoprotein cholesterol (OR, 1.32; 95% CI 1.06 to 1.64). CONCLUSIONS: In middle-aged adults, soft drink consumption is associated with a higher prevalence and incidence of multiple metabolic risk factors.