The diagnosis of pediatric diabetes mellitus (DM) traditionally is not considered a diagnostic specialty. However, considerable heterogeneity in the etiology of DM is seen among children and adolescents, making the recognition of discrete subgroups of DM very important for determining prognosis and appropriate treatment. The subgroups that result in non-insulin-dependent DM in children are as follows: the 'honeymoon' phase of type 1 DM, type 2 DM, genetic syndromes accompanied by DM, and maturity-onset diabetes of the young (MODY). The relative prevalence of these different subgroups depends on the population being studied. In the UK, in pediatric clinics where most patients are Caucasian, MODY is over 10 times more prevalent than type 2 DM. However, type 2 DM would predominate in a clinic where most children are from populations with a high prevalence of this condition (e.g. Asian Indians). It should be emphasized that MODY comprises two discrete clinical syndromes: glucokinase diabetes and transcription factor diabetes, the latter of which results from mutations in the genes encoding hepatocyte nuclear factor (HNF)-1alpha, HNF-1beta, HNF-4alpha and insulin promoter factor-1.