The objective of this systematic review was to evaluate the association between serum 25-hydroxyvitamin D (25OHD) and cardiometabolic risk in children and the effect of vitamin D supplementation on risk. We included 35 clinical trials, cross-sectional studies, case-control studies, and cohort studies that evaluated the relationship between 25OHD and blood pressure, lipid levels, insulin/glucose metabolism, endothelial dysfunction, and arterial stiffness. One randomized clinical trial that randomized adolescents to 2000 or 400 IU/d of vitamin D and found improvement in arterial stiffness in the high-dose group and worsening in the low-dose group. One cross-sectional study found no relationship between 25OHD and endothelial dysfunction. Of 12 cross-sectional studies, 10 found an inverse association between 25OHD and systolic blood pressure, although 2 trials found no relationship. There was no consistent association between 25OHD and lipid levels or insulin/glucose metabolism. Insufficient evidence was available to conclude that vitamin D supplementation yields cardiometabolic benefit.