African Americans have a greater prevalence than Caucasian Americans of hypertension, non-insulin-dependent diabetes mellitus, and cardiovascular disease. These conditions lead to substantial excess morbidity and mortality and are associated with and exacerbated by obesity, the prevalence of which is strikingly elevated in African American women. It is unknown if this increased prevalence of comorbid conditions is solely related to the greater prevalence of severe obesity among African American women, or due to differences in insulin sensitivity, glucose disposal, body composition, or fat cell metabolism. Through this project, we have verified that many of the physiological differences observed between African American and Caucasian adults are already present in obese children and in children at high risk for developing obesity. However, the roles that differences in energy expenditure, glucose metabolism, body composition, and other factors play in determining which children develop obesity and its comorbid conditions in adulthood remain unclear. In this study, we compare body composition, total and resting energy expenditure, and glucose disposal of obese African American and Caucasian children and of non-obese children of obese African American and Caucasian parents, to characterize the timing and nature of factors that may contribute to the prevalence of obesity and its complications. We also relate serum levels of the body-fat related circulating factors such as leptin, to these measures, and obtain samples for genomic DNA isolation from participants and their parents to characterize the roles of genes felt important for the development of obesity. We will follow these children for 15 years, studying them intensively at 5 year intervals until adulthood.