Obesity in children and adolescents should be seen as a chronic disorder and not merely as a biological variant. One aspect of the pathological significance of obesity in childhood and adolescence is determined by functional and individual limitation and psychosocial impairment. Another is the fact that these children and adolescents have a higher comorbidity, and appreciably increased morbidity and mortality rates in adulthood. The major causes of the condition are lifestyle related, in particular excessive intake of energy- and fat-rich foods together with increasingly inadequate exercise. In addition, however, there also appears to be a genetic predisposition that manifests as early and massive obesity in young years. Considerable importance attaches to the recording of height and weight development during regular examinations in the doctor's office. In addition, in particular the children of overweight parents, together with their families, should be instructed and advised on the need for a healthy and appropriate diet and regular exercise. In the case of extremely overweight children, a genetic investigation would be worthwhile.