PURPOSE: There are few rigorous studies about the side effects of antiepileptic drugs(AEDs) according to age. This study is to analyze differences of the side effects of AEDs in epileptic children according to age. METHODS: Sample are 368 children who had received AEDs for at least 1 month during January 1995 to June 1999. We reviewed their medical records including age, sex, AEDs and side effects, and analyzed these data by X2-test. RESULTS: Side effects were observed in 86(23.4%) of 368 patients. There was no difference in the frequency of overall side effects according to age. But significant differences existed in each side effect(p<0.05). The most common side effect according to age were hematologic side effect(75.0%) under 2 months, gastro intestinal side effect(41.7%) between 2 months and 1 year, CNS side effect(42.1%) between 1 year and 5 years, CNS side effect(41.5%) over 5 years. Hepatotoxicity, the increase of AST/ALT due to valproate, occurred significantly more frequently in children younger than 2 years(p<0.05). Drug eruption and post-carbamazepine leukopenia had no differences according to age. Under 1 year, valproate group had significantly more side effects in CNS. But carbamazepine, phenobarbital, and vigabatrin groups had no differences. CONCLUSION: There was significant difference in the side effects of AEDs among each system according to age. It is recommended to use valproate as monotherapy in children younger than 2 years, and pay more attention to CNS side effect in children older than 1 year.