Obesity in children at school age is an increasing problem in Peru. It concentrates in urban areas, mainly in Lima where one out of three children is overweight. An initial study in 80 schools in Lima showed that the lack of physical activity would have a greater impact on overweight and obesity in school children than the amount of food intake. More detailed studies are required. In spite of the limited information available regarding its determining factors, it is necessary to implement culturally-sensitive measures to fight this problem as part of the current nutritional policies, and prevent the problem from spreading, making sure the sustainability of the health system is not affected.