Over the past two decades, obesity in children has been increasing worldwide, leading to serious complications. The treatment for childhood obesity remains largely ineffective; therefore preventive measures are crucial. The prevalence of obesity depends on the BMI-percentiles used. Recent BMI-percentiles may underestimate the problem. Currently, the only representative cross-sectional BMI-data are obtained at the school entry examination. These data reveal certain risk groups (migrants, low socioeconomic status). More representative longitudinal data are needed to study the progression of obesity during childhood. Our obesity clinic provides multidisciplinary therapy programs (group or individual) and is also focused on the diagnosis and treatment of comorbidity, especially of the metabolic syndrome. Almost 60% of our severely obese patients are already affected. The molecular diagnosis of rare monogenetic or syndromal forms of obesity may be helpful in providing additional support for these patients. In general, most obesity programs are successful only in families without severe psychosocial problems and with motivation for lifestyle changes. This can be expected in only 3% of our families. Therefore, a substantial societal effort is needed to facilitate prevention for all children, and effective therapies have to be tailored depending on biological and psychosocial risk factors.