['To test the hypothesis that the concentration of non-high-density lipoprotein cholesterol (non-HDL-C) is associated with the metabolic syndrome (MetS) in youth.', 'Data on children and adolescents aged 12-19 years (n = 2734) from the cross-sectional National Health and Nutrition Examination Survey 1999-2004 were analyzed.', 'Depending on the definition of MetS used, the mean non-HDL-C concentration among youth with MetS ranged from 144.2 to 155.8 mg/dL, compared with 108.8-109.1 mg/dL in those without MetS (all P < .001). The MetS prevalence ranged from 6.9% to 11.7% in youth with a non-HDL-C concentration of 120-144 mg/dL and from 21.5% to 23.4% in those with a concentration ≥ 145 mg/dL-both significantly higher than the prevalence of 1.9%-3.4% in youth with a concentration <120 mg/dL (all P < .001). After adjustment for potential confounders, youth with a non-HDL-C concentration ≥ 120 mg/dL or ≥ 145 mg/dL were about 3 or 4 times more likely to have MetS compared with those with a non-HDL-C <120 mg/dL or <145 mg/dL (all P < .001).'] Is non-high-density lipoprotein cholesterol concentration associated with the metabolic syndrome among US youth aged 12-19 years?