Autism is a neuropsychiatric disorder of social, cognitive, and language development. Cerebellar abnormality in autism has been shown consistently from autopsy and magnetic resonance image (MRI) studies. A new MRI study with careful methodologic designs identified two subgroups of autistic patients: hypoplasia and hyperplasia of cerebellar vermian lobules VI-VII. The existence of these two subtypes was also supported via the meta-analysis of data from separate research groups. In addition to the cerebellar abnormality, recent MRI studies in autism demonstrated abnormalities in the parietal lobe and the posterior subregions of the corpus callosum where parietal cortical fibers are concentrated. Furthermore, neurobehavioral correlates of cerebellar and parietal abnormalities have also been investigated. In contrast, there is a lack of significant difference in the cross-sectional size of the posterior hippocampal formation between autistic and normal subjects, which is discrepant with predictions based on some autopsy studies.