The aim is to examine the effects of valproic acid on the metabolic parameters, body composition and anthropometric measurements. Non-obese patients diagnosed with idiopathic epilepsy were included in the study. Multifrequency bioelectrical impedance analysis, anthropometric measurements, fasting glucose, lipid levels, serum insulin levels and thyroid function tests were evaluated at the beginning, third and sixth months of valproic acid treatment. A total of 25 patients were investigated. The mean age of patients was 8.21±3.96 years. The body mass index of patients significantly increased during treatment. Fat mass, lean mass, basal metabolism rate, body fat mass index and fat free mass index values significantly increased and basal metabolism rate/body weight ratio significantly decreased during valproic acid treatment. Significant increase in thyroid stimulating hormone levels and significant decrease in free thyroxine levels occurred during the treatment.Conclusion: valproic acid leads to weight gain by both increasing fat and lean mass.