EDITOR'S NOTE:The problem of childhood obesity is accelerating throughout the world. The following is a position paper from The European Childhood Obesity Group (ECOG) that outlines the nature of the problem of childhood obesity along with treatment and prevention methods available today. The paucity of literature on prevention and treatment of obesity in children as documented in this paper points out the need for much additional research on obesity in children. OBJECTIVES: The awareness of childhood obesity as a major health problem and an uncontrolled worldwide epidemic has to be increased in the society. DESIGN: In order to improve the quality of the health care and to minimize the cost it is important to investigate and standardize pediatric obesity prevention and treatment and to adapt to social and cultural aspects. RESULTS: Obesity is the result of excess body fat. The different norms and definitions in Europe and the US is described and clarified. However, the available methods for the direct measurement of body fat are not easily used in daily practice. For this reason, obesity is often assessed by means of indirect estimates of body fat, that is, anthropometrics. There are essentially six relevant levels, which could be involved in prevention of child and adolescent obesity: family (child, parents, siblings, etc), schools, health professionals, government, industry and media. Evidence-based health promotion programs has to be given a high priority. Government should encourage media increase information about healthy nutrition and to avoid the marketing of unhealthy foods including sweet drinks, for example, in TV. Many different approaches of treatments of obesity have been investigated, including diet, exercise, behavioral therapy, surgery, and medication. None have been found to be effective enough as sole tools in children. This has led to focus on multidisciplinary programs especially involving families. Behavioral cognitive therapy is effective in treating childhood obesity as is family therapy. Surgery and drug treatment cannot be recommended without additional research. Clinicians should consider the various factors that can influence body composition. CONCLUSION: It is important to know and to follow nutritional factors, energy intake and composition of the diet, nutrition and hormonal status, food preferences and behavior, and the influence of non-nutritional factors. We recommend that obesity should be the major priority both in the health care system, on the scientific level and for future political actions.