The size of the seven subregions of the corpus callosum was measured on MRI scans from 22 non-mentally retarded autistic subjects and 22 individually matched controls. Areas of the anterior subregions were smaller in the autistic group. In a subsample, measurements were adjusted for intracranial, total brain, and white matter volumes and the differences between groups remained significant. No differences were found in the other subregions. This observation is consistent with the frontal lobe dysfunction reported in autism.