Background: Childhood metabolic syndrome (MetS) has been found to predict adulthood MetS, type 2 diabetes and cardiovascular disease, emphasizing the early identification of children at increased risk of these diseases. Children with clustering of metabolic risk factors have been reported to have a mild arterial stiffness and endothelial dysfunction, but limited evidence is available from population-based samples of children. Methods and Results: The associations of metabolic risk factors with arterial stiffness, tone and endothelial function were studied in 173 prepubertal children (90 girls) 6–8 years of age. MetS was assessed both by continuous MetScore and dichotomously. Stiffness index (SI), reflection index (RI) and finger skin temperature (FST) were measured before and after maximum exercise test, and percent change was calculated for RI (RI%Δ) and FST (FST%Δ). MetScore (r=0.26, P=0.001), fasting insulin (r=0.24, P=0.002), fasting triglycerides (r=0.20, P=0.009), systolic (SBP; r=0.24, P=0.002) and diastolic blood pressure (DBP; r=0.19, P=0.013) correlated with SI. MetScore (r=–0.17, P=0.024, r=0.21, P=0.006), waist circumference (r=–0.19, P=0.012, r=0.23, P=0.003) and SBP (r=–0.16, P=0.035, r=0.21, P=0.005) correlated with RI and FST. High-density lipoprotein cholesterol correlated with FST (r=–0.22, P=0.004) and FST%Δ (r=–0.24, P=0.002). RI decreased and FST increased with exercise (P<0.001). Waist circumference correlated inversely with RI%Δ in boys (r=–0.22, P=0.046) and directly with RI%Δ in girls (r=0.27, P=0.011). Conclusions: Metabolic risk factors are associated with arterial stiffness, tone and endothelial function in prepubertal children.  (Circ J 2013; 77: 1281–1288)