Among children and adolescents, metabolic syndrome (MetS) is more common than previously believed. Hence, any information on the relation between vitamin D insufficiency/deficiency and insulin resistance (IR) in this population with risk of developing MetS is of great importance. This review analyzes and evaluates the existing evidence from cross-sectional, observational, and retrospective studies concerning the effect of vitamin D insufficiency/deficiency on MetS as a whole or on its various components. Most data show that insufficient vitamin D status is associated with increased prevalence of MetS or its individual components, mainly blood pressure and IR, often independent of overall obesity or abdominal adiposity. The implications of these findings could be associated with increased risk for developing cardiovascular disease and type 2 diabetes mellitus in later life. The very few randomized control trials examining any possible beneficial effects of vitamin D supplementation are also included.