The authors realise a synthesis on classical data and recent pathogenic explanations in childhood obesity. The obesity is a nutritional disorder of great interest nowadays and surpasses the incidence of the major problem of pediatrics until now--the malnutrition. There is documented data concerning the global incidence of obesity which is continuously growing when it comes to children. That is why the prophylaxis must become a priority by using measures in the first period of life (natural feeding, the need of late diversification, the avoidance of hyperproteic diets). The recent pathogenic data and the long term populational studies change the old conceptions regarding the risk of some categories of children. Thus mother's malnutrition, the low birth weight, children that followed hyperproteic diets paradoxically represent categories of risk for obesity. A recent recorded phenomenon, which amplifies the risk for obesity is the early adiposity rebound which is recorded nowadays even for ages lower than five years. There are described the hormonal mechanisms involved in appetite and satiety up to the receptor level: leptin, ghrelin, adiponectin, endocannabinoid receptors. There are pointed out all the long term risk elements (high birth weight, low birth weight, the pregnant woman's nutrition) and the modern medical treatments for obesity.