OBJECTIVES: The purpose of this study was to investigate the association of metabolic syndrome (MetS) with subclinical atherosclerosis, determined by ultrasound carotid intima-media thickness (CIMT) measurements, in young adults. BACKGROUND: Metabolic syndrome is associated with subclinical atherosclerosis and increased cardiovascular risk in older and middle-aged adults; however, these associations have not been studied among young adults. METHODS: Non-diabetic subjects from Bogalusa Heart Study, a longitudinal study of atherosclerosis in young adults, underwent B-mode ultrasonography of the carotid arteries. Metabolic syndrome was defined with the National Cholesterol Education Program Adult Treatment Panel III (MetSNCEP) and World Health Organization (MetSWHO) definitions. CIMT and MetS associations were evaluated with multivariable regression and area under receiver-operator characteristic curve (AUC) analyses. RESULTS: Of 507 subjects (29% black, 39% male, mean [SD] age 32 [3] years), 67 (13%) had MetSNCEP and 65 (13%) had MetSWHO. Common (mean = 0.70 [0.11] mm vs. 0.66 [0.08] mm, p = 0.002) and internal CIMT (0.72 [0.21] mm vs. 0.68 [0.12] mm, p = 0.020) were higher among those with MetS(NCEP) than those without MetS(NCEP). Common (0.69 [0.11] mm vs. 0.66 [0.08] mm, p = 0.020) and internal CIMT (0.73 [0.23] mm vs. 0.68 [0.12] mm, p = 0.012) also were higher among those with MetSWHO than those without MetSWHO. Composite CIMT increased with the number of MetS components present (MetSNCEP r = 0.997, p < 0.001; MetSWHO r = 0.946, p = 0.053). Metabolic syndromeNCEP (AUC = 0.557, 95% confidence interval [CI] 0.513 to 0.601) and MetSWHO (AUC = 0.539, 95% CI 0.495 to 0.584) both predicted composite CIMT > or =75th percentile. CONCLUSIONS: In young adults, MetS is associated with increased atherosclerotic burden, and therefore, increased cardiovascular risk. These results support the importance of screening and early intervention in this population.