PURPOSE: The diagnosis of cortical dysplasia(CD) and microdysgenesis(MD) is valuable because they often cause childhood intractable epilepsy. This study is to analyze clinical manifestations, EEG findings, and imaging features based on the pathologic diagnosis(cortical dysplasia and microdysgenesis) in childhood intractable epilepsy with surgical treatment. METHODS: We performed retrospective studies and analyzed 27 patients with MCD diagnosed by pathologic findings after brain lobectomy for intractable epilepsy from October 2003 to September 2006 in our hospital. We compared their clinical characteristics, EEGs, neuroimaging studies including MRI, and FDG-PET. We analyzed the locations of malformations of cortical development(MCD). The surgical outcomes were reviewed. RESULTS: There were no pathognomonic seizure types or EEG findings for microdysgenesis. The clinical and EEG features of microdysgenesis were similar to those of cortical dysplasia. Only 6(37 percent) out of 16 microdysgenesis patients showed normal MRI findings and also 2(18 percent) out of 10 cortical dysplasia patients showed normal MRI findings. The most common location of MCD was frontal lobe in both of the groups, followed by temporal lobe. 10(63%) out of 16 microdysgenesis patients and 9 (90%) out of 10 cortical dysplasia patients became seizure free. The locations of MCD was not related to the prognosis of the outcomes. All the patients who had had developmental delay showed improvement in development after the surgery. CONCLUSION: There were no significant differences in gender, seizure onset age, duration of seizures, seizure types, EEG findings, and MCD locations between CD and MD. The seizure outcomes were better in CD than in MD. All the patients whose pre- and post-oprative developmental status were compared showed developmental improvement.