Obesity became a global epidemic. Similarly, the global prevalance of childhood and adolescent obesity dramatically increased after the 1990s. A number of consequences of childhood and adolescent obesity are seen in this period and later in life. These problems are dyslipidaemia, hypertension, cardiac abnormalities, endothelial dysfunction, fatty liver disease, hyperinsulinemia, insuline resistance, type 2 diabetes, psychological problems, pubertal disorders, and economic burden. Obesity is one of the most important risk factor for developing type 2 diabetes in adolescents as in addition to genetic and ethnic factors. Therefore the prevention of adolescent obesity and type 2 diabetes is an important task of pediatricians.