OBJECTIVE: The purpose of this study is to evaluate the effect of the corpus callosotomy and to elucidate possible prognostic factors. METHODS: The cases of 39 patients who underwent corpus callosotomy were reviewed retrospectively. Clinical outcomes were analyzed using Engel's classification, with consideration of various presurgical conditions and the extent of the callosal resection during follow-up more than one year. RESULTS: Satisfactory outcome (Engel's class I, II) was obtained in 20 patients (51%) of 39 patients. In 36 cases with drop attack seizures, the class I, II outcomes were 22 patients (61%). When the patients were grouped according to the extent of callosal resection, the class I, II outcomes were 50% of the patients with anterior 1/2 or 2/3, 50% of those with anterior 4/5 callosotomy, and 57% of those with total callosotomy, respectively. The mean follow-up period was 34 months (24 to 58 months). CONCLUSION: Although it is not statistically significant, the patients who had underwent total callosotomy show better outcomes than those with partial callosotomy. Corpus callosotomy is efficacious in controlling medically intractable epilepsy in appropriately selected patients.