The prevalence of pediatric obesity is increasing at an unprecedented rate. Obese children are at risk for the development of insulin resistance, relative insulin deficiency and type 2 diabetes mellitus. However, the cause of insulin resistance remains an area of scientific interest. The study of type 2 diabetes in children is limited by the lack of a non-invasive method to evaluate insulin resistance. Recent studies have suggested that mitochondrial dysfunction is associated with, and perhaps predictive of insulin resistance in adult relatives of individuals with type 2 diabetes. Mitochondria generate energy in muscle tissue through the production of ATP, and are important in the metabolism of both glucose and fat. This study evaluates a novel, non invasive, safe method for predicting insulin resistance and diabetes in children using a magnetic resonance imaging (MRI) based technique to measure mitochondrial function. We propose to investigate mitochondrial function and glucose metabolism in obese and non-obese children in early, mid and late puberty. Analyses will be conducted to investigate the presence of mitochondrial dysfunction in obese children, to evaluate the contribution of mitochondrial dysfunction to insulin resistance, and to determine the contribution of pubertal status to mitochondrial dysfunction and insulin resistance. The successful completion of this study would provide evidence to support the hypothesis that mitochondrial dysfunction plays a role in insulin resistance and diabetes in children. In addition, it would provide a new technique for the prediction of disease states and perhaps lead to the development of preventative therapeutics for insulin resistance and type 2 diabetes in children.