Valproic acid (VPA) is an antiepileptic drug, used for focal and generalized seizure. VPA treatment resulted in significant weight gain but there are no systematic data about the prevalence of this side effect. The aim of the study was to evaluate the weight gain of a pediatric population with epilepsy. We enrolled 38 patients, 17 females and 21 males with a mean age of 8.2±4.4 years. We evaluated data about height, weight and BMI at beginning of treatment and at 24, 36 and 48 months of follow-up. There is a statistically significant difference between the percentile value of weight and BMI at baseline and at 36 and 48 months of follow-up (P<0.01) but there is not statistically significant difference between the percentile value of height (P=0.22 and P=0.18). We believe that a nutritional support should be guaranteed to the pediatric patients with epilepsy that begin the VPA therapy.