The incidence of overweight and obesity among children has increased dramatically in recent decades, with about one-third of children in the U.S. currently being either overweight or obese. Being overweight in early childhood increases risk for later obesity. There is evidence for the efficacy of family-based behavioral treatment to control weight and improve health outcomes. Obesity-related health risks have been documented, including metabolic syndrome. There is also increasing incidence of type 2 diabetes (T2D) among youth in recent years, with obesity and family history of T2D generally present. Lower income and ethnic minority status are associated with both obesity and T2D in youth. Most youth with T2D do not achieve optimal glycemic control, and are at high risk for later health complications. Obesity and T2D represent significant public health issues with potentially great personal and societal cost. Research addressing the prevention of obesity and T2D among youth is urgently needed.