Diabetes mellitus is a complex chronic disorder characterized by changes in the carbohydrate, fat, and protein metabolism, leading to hyperglycemia. Diabetes is classified into four main groups: diabetes mellitus type 1, diabetes mellitus type 2, gestational diabetes, and other non-specific types of diabetes. Type 1 diabetes mellitus is the most common type of diabetes in children. It is caused by the destruction of beta cells of the pancreas, which leads to an absolute lack of insulin. Genetic and environmental factors are responsible for the development of the disease, which lead to disturbances in the immune system and the creation of antibodies. The incidence of type 2 diabetes mellitus is increasing due to the increasing number of obese children in the world. The pathophysiological basis of the disease is the emergence of insulin resistance in various tissues. Maturity-onset diabetes of the young (MODY) is inherited in an autosomal dominant manner. The disease occurs in children who, as a rule, are not obese, adolescents and young adults. The classic symptoms of diabetes are polyuria, polydipsia, polyphagia, weight loss, fatigue, and blurred vision.