We performed proton magnetic resonance spectroscopy of the mesial temporal regions in 20 children with intractable temporal lobe epilepsy and compared results with those from 13 normal subjects. Abnormalities of the ratio of N-acetylaspartate to choline plus creatine (NAA/[Cho+Cr]) were seen in 15 patients (75%). The ratio NAA/(Cho+Cr) was correctly lateralizing in 55% and incorrectly lateralizing in none. Bilateral abnormalities were seen in 45%. Overall there was a unilateral decrease in N-acetylaspartate on the side ipsilateral to the seizure focus (mean 19% decrease vs normals, with 5% decrease on the contralateral side), suggesting neuronal loss or dysfunction. There was also a bilateral increase in creatine and choline (mean 18%), consistent with reactive astrocytosis. We conclude that proton magnetic resonance spectroscopy can contribute to lateralization of the seizure focus, and by detection of bilateral abnormalities, can contribute to the understanding of the underlying pathophysiology in temporal lobe epilepsy.