Diabetes mellitus is one of the leading public health problems, both in the world and in the Republic of Croatia. The occurrence of diabetes in children and young people is a particularly big problem. It is a group of metabolic disorders characterized by elevated blood glucose levels as a result of insufficient insulin secretion, lack of action or a combination of these two mechanisms. It is of multifactorial origin, an autoimmune disease in which the beta cells of the pancreatic islets of Langerhans are partially or completely destroyed. Several forms of diabetes can occur in children, of which the most common are type 1 and type 2. Diabetes mellitus type 1 or insulin-dependent is one of the most common chronic health conditions in children under 18 years of age. With the obesity pandemic, we are witnessing an increasing incidence and occurrence of non-insulin-dependent diabetes mellitus type 2, already at that age. It is very important to know the origin, causes, development and complications of this disease, because it affects the choice of treatment regimen, as well as procedures to combat the complications of this disease. The main therapy includes insulin replacement therapy, and in addition to human insulin, analogous forms of insulin, stem cell therapy, transplantation of Langerhans islets of donor pancreas are also being investigated. With proper health care, adjustment of diet, adjustment of meals and levels of physical activity with insulin therapy, it is possible to achieve a satisfactory quality of life in sick children. Although insulin therapy remains the main choice in the treatment of diabetes, it is to be expected that further research in the field of diabetes will bring new more successful solutions in the treatment of the disease, especially solutions related to Langerhans pancreatic islet transplantation.