A clinical and neuroradiological study was carried out to clarify the relationship among cerebral dysgenesis, psychomotor retardation and neonatal epilepsy. Twenty-one cases with epilepsy developed within four weeks after birth were selected among 770 in-patients with childhood epilepsy. They consisted of one benign familial neonatal convulsion, nine of early myoclonic encephalopathy, four of Ohtahara syndrome, six of symptomatic localizationrelated epilepsy, and one of undetermined epilepsy. Seven cases with non specific types of epilepsies were investigated in detail. They developed into four of frontal lobe epilepsy, one of temporal lobe epilepsy and one severe epilepsy with multiple independent spike foci. Psychomotor retardation was observed in six of seven cases, and cerebral dysgenesis was considered to be important as an etiological factor. Proton MR spectroscopy revealed the decrease in the ratio of N-acetylaspartate/choline in the area with heterotopic gray matter and in the side of hemimegalencephaly, contrasted with a contralateral area without lesions. These findings can be inferred to reflect the decreased numbers of neuronal cell population or reduced metabolism in the lesions.