Background: Vitamin D deficiency is a concern in the US. Association between vitamin D status and metabolic syndrome (MetS), insulin resistance (IR), and inflammation is unclear in children. Objective: The relationship between serum vitamin D and MetS, C-reactive protein (CRP), and Homeostatic Model Assessment-IR (HOMA-IR) was investigated. Design: Data from 3 cycles of National Health and Nutrition Examination Survey, 2001-2006 for 3700 (1820, boys; 1880, girls) children and adolescents, aged 12-17 y were used to assess prevalence of vitamin D deficiency (<20 ng>/mL) and association between serum vitamin D and prevalence of MetS, various components of MetS, CRP, and HOMA-IR using multivariate regression models. Results: Overall, prevalences of MetS and vitamin D deficiency were 6.1% and 30.5%, respectively. Prevalence of vitamin D deficiency was higher in girls (52%), blacks (74%), non-supplement users (50%), persons who were examined in winter (56%), and persons in the low poverty income ratio group (57%) compared to their counterparts. Serum vitamin D was inversely associated with waist circumference (P<0.001), systolic blood pressure (P=0.009), and HOMA-IR (P=0.003) and positively associated with HDL-cholesterol (P<0.001). Children with lowest serum vitamin D are at increased risk for MetS (P=0.04; OR 2.26; 95% CI: 1.11, 4.61). Serum vitamin D was not related to CRP (P<0.10). Conclusions: Children with poor vitamin D status are at increased risk for MetS and IR. Because of negative health outcomes associated with MetS and poor vitamin D status when existed individually or in combination, early detection and intervention of these conditions are paramount, especially in children.