Due to economic growth, and as lifestyles got more convenient, the number of calories being spent has decreased for two reasons. One is the lack of physical activities and the other is the increased consumption of westernized food. This outbreak of obesity is the highest among the children and the adolescents. Among primary, middle, and high school students in seoul, the prevalence of obesity has increased from 6.2% in 1988 to 17.9% in 2002 in boys, and from 6.5% to 10.9% during the same period in girls. Thus, during the last 14 years, the obesity frequency increased 2.9 times in boys, and 1.7 times in girls. Increase of child obesity is a worldwide tendency. In United States, 20% of all children, 27% of all adolescents, and 33% of all adults are obese. Childhood obesity is catching much attention, because it has physiological and psychological damages for long term as well as for short term. Some of the psychological damages of an obese children are having difficulties with familial and friend relationships, also having a low self-esteem. Although, physiological damages in short term are not clear, the long term damages would have progressed from an early age up to an adult. Detection and treatment of overweight and obesity in childhood are important not only from the aspect of preventive pediatrics, but also the public health that in which include child's physical, social, and psychological health as well as the negative effect it will have on the adults.