Diabetes mellitus is one of the most often chronic diseases in children. It is classified into four categories: type 1, type 2, other specific types and gestational diabetes. Diabetes mellitus type 1 and dibetes mellitus type 2 are most common in children, and they are products of genes and enviromental triggers. Fasting plasma glucose level, random plasma glucose test, oral glucose tolerance test and glycated hemoglobin (Hb A1C) are used for the diagnosis of diabetes. The classic symptoms of untreated diabetes are weight loss, polyuria, polydipsia , polyphagia, weight loss and fatigue. Children with diabetes mellitus type 2 are obese and they are under higher risk to develop comorbidities. Treatment of diabetes mellitus type 2 includes lifestyle modification, weight loss, physical exercise and metformin. The menagment of diabetes mellitus type 1 in children includes insuline. Complications related to diabetes mellitus can be acute and chronic. Acute complications are hypoglikemia, hyperglikemia and diabetic ketoacidosis. Vascular complications are most common chronic complications and they become clinical in adulthood. Vascular complications include diabetic nephropathy, retinophaty, neurophaty, and cardivascular disease. Diabetic ketoacidosis is the most severe acute complication of diabetes mellitus and children with diabetic ketoacidosis require hospitalization, rehidration and insulin replacment therapy.