The increase in the incidence of type 1 diabetes (T1D), especially in children <5 years of age reported over the past decade can be attributed to changes in environmental factors, either quantitative or qualitative, rather than to an effect of genetic factors operating in such a short period of time. The notable increase in the incidence of type 2 diabetes (T2D) in children and adolescents is very likely the consequence of the increase in obesity and sedentary life style occurring in developed countries. The increase in the number of children and adolescents with a mixture of the two types of diabetes has recently come to light (i.e. subjects who are obese and/or with signs of insulin resistance as well as positive for markers of autoimmunity to beta cells). Under the current classification, it is difficult to define the type of diabetes affecting these young subjects, being classified as T2D because they are obese and insulin resistant, but also as T1D because of the presence of auto-antibodies to beta cells. There is no doubt that these subjects show an overlapping diabetes phenotype typical of both T1D and T2D suggesting that the current classification of diabetes should be revised taking into account this new form of diabetes which has called double diabetes or hybrid diabetes.