A dramatic increase in the prevalence of overweight and obesity among children in Europe has occurred in the last twenty years, especially the last ten years. The number of overweight children is increasing in the EU by at least 400,000 every year, of which 85,000 are obese. Prevention of further cases is a priority, but the evidence base for child obesity prevention is limited in scope and provides only a few general observations. Prevention will probably require policies that affect not only the family and the school but also affect the wider social context, such as controls on marketing to children and improved safety in the built environment. Scientists and physicians can help to influence policy makers through their professional organisations.