Childhood obesity results from excessive dietary intake as compared with energy expenditure. This imbalance can result from either overeating or a constitutional decrease in one or several of the components of energy expenditure: resting metabolic rate, diet-induced thermogenesis, or exercise-related thermogenesis. Decreased energy expenditure is probably at least partly genetic in origin, contributing to the significant clustering of obesity in families. Management aims at reducing the imbalance by decreasing the caloric intake. Once the desired weight is achieved, intake must be adjusted to expenditure to avoid weight regain.