Abstract: The increase in the incidence of type 1 diabetes (T1D), especially in children <5 yr 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 an increasing sedentary lifestyle and an increase in obesity, which has been occurring in developed countries. An 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 β cells), although the epidemiological data supporting such a conclusion are sparse. Under the current classification, it is difficult to define the type of diabetes affecting these young subjects, who might be classified as T2D because they are obese and insulin resistant but also as T1D because of the presence of autoantibodies to β cells. These subjects show an overlapping diabetes phenotype typical of both T1D and T2D, suggesting that the current classification of diabetes should be revised to take into account this new form of diabetes, which has been called ‘double diabetes’ or ‘hybrid diabetes’. In this review, we report recent findings on the increasing rates of all forms of diabetes in the young population, including unpublished data collected in Russia.