We prospectively examined the effects of valproic acid on the endocrine system and metabolic variables in epileptic children. Patients with newly diagnosed idiopathic epilepsy were included in the study. Laboratory and clinical variables were assessed before and after 6 and 12 months of treatment. In total, 30 patients (mean age, 8.6 +/- 4.4 years S.D.) were investigated. Body mass index and body mass index standard deviation scores of patients increased significantly during treatment. Although there was no statistical significance regarding fasting glucose, serum insulin, triglyceride, and high-density lipoprotein cholesterol levels and the insulin resistance index, a statistically significant increase in total and low-density lipoprotein cholesterol levels had occurred after 12 months of valproic acid treatment. At the end of the study period, four patients were obese, and six patients were overweight. There was a significant correlation between serum levels of valproic acid and body mass index at month 6 of treatment. There was no significant change in androgen hormone levels during treatment in the prepubertal group. Body mass index and body mass index standard deviation scores increased during the first 6 months of valproic acid treatment. Patients treated with valproic acid should be regularly followed for obesity.