We reported a case of type I lissencephaly/pachygyria which had cystic changes in the periventricular white matter and lentiform nuclei. The patient developed neonatal seizures and was referred to Anjo Kosei Hospital His seizures were frequent and refractory to anticonvulsants. His development was severely retarded. CT and MRI revealed cystic changes in the periventricular white matter and lentiform nuclei as well as bilateral diffuse pachygyria and agenesis of corpus callosum. He died of unknown cause at 5 months of age and postmortem examination was performed. Type I lissencephaly/pachygyria, almost complete agenesis of corpus callosum, leptomeningeal glioneuronal heterotopia and hypoplasia of corticospinal tract were seen pathologically. Marked gliosis and CD 68 positive macrophages were found around the cystic lesions in the periventricular white matter and lentiform nuclei, which suggests that these lesions were the secondarily destructive lesion. We considered that these secondary lesions were due to frequent seizures which could cause insufficient supply of blood and glucose in those areas.