PURPOSE: A number of drugs are capable of changing body weight as a side effect. A number of neurotransmitter systems acting in several hypothalamic nuclei are pivotal to the storage regulation of body fat. Leptin is a protein encoded by the ob gene that is expressed in adipocyte. It regulates eating behavior by activating the action to the satiety center in the hypothalmus. The purpose of this study is to investigate the changes of serum leptin in children with epilepsy. METHODS: Serum leptin levels were measured in 43 epileptic patients (30 males, 13 females) receiving valproate or carbamazepine by radioimmunoassay. Thirty patients (19 males, 11 females, 10.0+/-5.0 years of age) were treated with valproate (VPA group) and 13 patients (11 males, 2 females, 9.1+/-4.0 years of age) were treated with carbamazepine (CBZ group). Obesity index and body mass index were calculated before and during anticonvulsant medications. RESULTS: 1) Body mass indices were significantly increased after VPA or CBZ medication; from 17.24+/-2.74 to 18.47+/-2.60 in VPA group, from 16.77+/-1.69 to 17.43+/-3.01 in CBZ group. 2) Obesity indices were increased without statistical significance after medication in both group. 3) Serum leptin levels were significantly higher in VPA group (4.54+/-4.77ng/ml) than CBZ group (2.47+/-2.26ng/ml). CONCLUSION: Body weight gain after VPA medication in susceptible individual might be related to a certain mechanism that elevates serum leptin level.