Prevalence of childhood overweight and obesity have dramatically increased worldwide in the last decades. Overweight and obesity are the result of a complex interaction between genetic and environmental factors. The aim of our longitudinal study was to assess the prevalence of overweight and obesity in a population of Italian schoolchildren followed for 2 years and to identify main risk factors for obesity onset and persistence in childhood. We enrolled 632 children (males /females= 345/287), aged 3 to 8 yr.Weight and height were measured at time 0, 1 (1 yr later), and 2 (2 yr later). Overweight and obesity were defined using body mass index (BMI) (Italian growth charts). Data collected included: birth weight, gestational age,maternal weight gain during pregnancy, breast feeding, parents' BMI, educational level, and occupation type. At time 0, 1, and 2 the prevalence of overweight was 22%, 22%, and 25%, respectively, and the prevalence of obesity was 7%, 8%, and 8%, respectively. During follow-up 62%of children remained normal weight, 24% was always overweight or obese, 9% became overweight, while only 5% of overweight subjects became normal weight. Male gender, maternal weight gain during pregnancy >10 kg, parental overweight/obesity were positively associated with the presence of overweight during the entire follow-up. On the contrary, being small for gestational age at birth was negatively related to persistence of overweight. No influence was found for being breastfed, for parental low educational level, and manual occupation. A large prevalence of overweight/obesity was observed in Italian schoolchildren. Gender, maternal weight gain during pregnancy, and parents' BMI were the strongest predictors of the persistence of child overweight and obesity.