Childhood obesity is the most common nutritional disorder in the industrialized countries. The incidence and the prevalence of childhood obesity is continuously increasing also in the developping countries. Childhood obesity tends to persist into adulthood and is associated to several metabolic and non metabolic disorders. Unfortunately, treatment of obesity is discouraging and most of obese children are not able to lose weight and to avoid obesity relapse after weight loss. Parents' obesity, high and low birth weight, sedentary behaviour, high fat-high sugar diet, are the main obesity risk factors. Prevention seems to be a necessary tool for contrAsting obesity epidemic. Several prevention programs are ongoing and their efficacy will be tested.