PURPOSE: Ketogenic diet(KD) is an alternative treatment for children with intractable seizures. This study was performed to evaluate the efficacy and tolerability of ketogenic diet METHODS: A retrospective study was performed for 57 patients(31 males, and 25 females), who were enrolled in a ketogenic diet program from 1998 to 2003 in Seoul National University Children's Hospital. We investigated the overall efficacy, influencing factors such as age at diet onset, seizure type, initial fasting, adverse events and reasons for discontinuing the diet. RESULTS: The patients mean age at diet onset was 3.5 years old. They had 3.14 medications on average at the diet initiation. One month after the diet initiation, 49 of 57(86 %) remained on KD, with 37(64.9%) having more than 50% seizure reduction rates. At 6 months, half of the patients remained on KD, with 14(28%) seizure free and 22(44%) having more than 50% seizure reduction rates. At 12 months, 15 patients(34.9%) remained on KD, with 14(32.6%) having more than 90% seizure reduction rates. Seizure types, initial fasting and age at diet onset were not statistically related to the outcomes. There were a few complications during the diet. The most common reasons for discontinuing KD were ineffectiveness and poor tolerability. CONCLUSION: Ketogenic diet appears to be a relatively effective and safe treatment option for children with intractable epilepsies.