The prevalence of overweight and obesity in children is increasing significantly. This increase is attended by an increase in diabetes type 2 in children and adolescents. The most important risk factor for the rise of insulin resistance amongst young people is overweight. The diagnostic criteria for diabetes mellitus in young people are: (a) symptoms of diabetes mellitus and a random plasma-glucose concentration of > or = 11.1 mmol/l, or (b) fasting plasma-glucose concentration of > or = 7.0 mmol/l, or (c) 2-hour plasma-glucose levels following an oral glucose-tolerance test > or = 11.1 mmol/l. Treatment involves lowering the glucose concentration by changes in lifestyle such as more physical exercise and dieting. In the US, metformin is registered for use in young people. Insulin is indicated in cases of serious hyperglycaemia or diabetic ketoacidosis. Early detection is very useful in obese children with two additional risk factors: diabetes type 2 in first- and second-degree relatives, members of certain ethnic groups or indications of insulin resistance.