Changes in food consumption and exercise are fuelling a worldwide increase in obesity in children and adolescents. As a consequence of this dramatic development, an increasing rate of type 2 diabetes mellitus has been recorded in children and adolescents in the USA and, more recently, in many countries around the world. Both genetic and environmental factors contribute to the pathogenesis of type 2 diabetes. Lower susceptibility in white Caucasians and higher susceptibility in Asians, Hispanics and blacks have been noted. There is a high hidden prevalence and a lack of exact data on the epidemiology of the disease in Europe: in Germany only 70 patients below the age of 15 years were identified in the systematic, nationwide DPV (Diabetessoftware für prospektive Verlaufsdokumentation) diabetes survey, but our calculations suggest that more than 5000 young people in Germany at present would meet the diagnostic criteria of type 2 diabetes. In Australasia, the prevalence of type 2 diabetes is reportedly high in some ethnic groups and again is linked very closely to the obesity epidemic. No uniform and evidence-based treatment strategy is available: many groups use metformin, exercise programmes and nutritional education as a comprehensive approach to treat type 2 diabetes in childhood and adolescence. The lack of clear epidemiological data and a strong need for accepted treatment strategies point to the key role of preventive programmes. Prevention of obesity will help to counteract the emerging worldwide epidemic of type 2 diabetes in youth. Preventive programmes should focus on exercise training and reducing sedentary behaviour such as television viewing, encouraging healthy nutrition and supporting general education programmes since shorter school education is clearly associated with higher rates of obesity and hence the susceptibility of an individual to acquire type 2 diabetes.