There have been marked changes in the epidemiology of diabetes in young people recent decades, with observed trends supporting our current understanding that type 1 diabetes results from an interaction from environmental factors and genetic predisposition. Overall, there has been a steady rise in the incidence of type 1 diabetes in children aged < 15 years, particularly since 1990, although there is some evidence for a plateau in incidence in some studies. The greatest increases have been observed in developing countries and in younger children (aged < 5 years), although findings are inconsistent. While countries of very high incidence have typically observed a male gender bias in type 1 diabetes incidence, the majority of studies have observed similar rates in males and females. The proportion of individuals with high risk HLA genotypes has decreased over time, suggesting an increasing role for environmental agents in the development of type 1 diabetes. Rates of type 2 diabetes in youth have also increased worldwide, in parallel with the rise in childhood obesity. Nevertheless, type 2 diabetes remains relatively uncommon in children, particularly before puberty. In many countries including Australia, it accounts for a lower proportion of diabetes (~ 10% or less) in young people compared with type 1 diabetes, with the exception of specific at-risk ethnic groups. These include Indigenous Australian and Canadian, American Indian, African American, Taiwanese, Japanese and Maori/Pacific Islander. Type 2 diabetes is typically more common in female adolescents compared to males, with rates in girls ranging from 10–70% higher than in boys. The heterogeneity of childhood diabetes is further evidenced by our greater understanding of the molecular genetics of monogenic and neonatal diabetes, although these represent a small proportion of childhood diabetes overall. Nevertheless, population based diabetes registries, along with studies of genotype/phenotype correlations, have made a significant contribution to our knowledge of the aetiology and outcomes of childhood diabetes.