PURPOSE: The efficacy of ketogenic diet in intractable childhood epilepsy has been reported in Korea. The aim of this retrospective study is to elicit the clinical and electrophysiological characteristics of intractable chilhood epilepsy, who can be successfully treated by ketogenic diet and to determine the favorable outcome group for ketogenic diet in intractable chilhood epilepsy. METHODS: We investigated clinical seizure type, epilepsy classification, underlying etiologies, clinical characteristics, EEG findings, response to treatments, and prognosis were studied in 41 patients with complete seizure remission over 6 months after ketogenic diet as compared with unsuccessful group among 96 patients of trial from July 1995 to October 1999 at the pediatric department of and epilepsy center at Sang-gye Paik Hospital, Inje University. RESULTS: 1) Complete seizure remission over 6 months were obtained in 15 patients of infantile spasms (IS), 6 cases of Lennox-Gastaut syndrome (LGS), 4 cases of periodic spasms, 3 cases of severe myoclonic epilepsy in infancy (SMEI), 1 case of Landau-Kleffner syndrome, 8 cases of other type of partial epilepsies. 2) Ketogenic diet was more effective in infantile spasms and periodic spasms but least effective in Lennox-Gastaut syndome. 3) In same types of epilepsies, ketogenic diet was more effective in patients with less frequent seizures, less severe EEG findings and earlier controlling seizures. CONCLUSIONS: Ketogenic diet was most effective in infantile spasms, patients with less frequent seizure in same type of epilepsy, less severe EEG findings in same seizure type, and patients who seizures stopped sooner after administration of ketogenic diet.