Diabetes mellitus is one of the most common severe chronic diseases of childhood. Much of our knowledge of the epidemiology of diabetes in young people has been generated by large collaborative efforts based on standardized registry data, such as the DIAMOND Project worldwide and the EURODIAB study in Europe. These registries showed that although at the start of the 20th century childhood diabetes was rare, by the end of the century a steady increase in incidence had been reported in many parts of the world. However, epidemiologic data for temporal trends in pediatric diabetes are still lacking or are minimal for most of the global population of youth, including in the United States. In addition, the epidemiology of diabetes in youth is changing. As youth are becoming increasingly overweight, we are seeing more obese children with a clinical phenotype of type 2 diabetes or "adult-onset" diabetes. It is imperative that efforts directed at surveillance of diabetes in young people continue and expand, not only to understand its complex etiology, but also because of its increasing public health importance.