• In seeking the neurologic substrate of the autistic syndrome of childhood, previous studies have implicated the medial temporal lobe or the ring of mesolimbic cortex located in the mesial frontal and temporal lobes. During an acute encephalopathic illness, a clinical picture developed in three children that was consistent with infantile autism. This development was reversible. It was differentiated from acquired epileptic aphasia, and the language disorder was differentiated from aphasia. One child had rises in serum herpes simplex titers, and a computerized tomographic (CT) scan revealed an extensive lesion of the temporal lobes, predominantly on the left. The other two, with similar clinical syndromes, had normal CT scans, and no etiologic agent was defined. These cases are examples of ah acquired and reversible autistic syndrome in childhood, emphasizing the clinical similarities to bilateral medial temporal lobe disease as described in man, including the Klüver-Bucy syndrome seen in postencephalitic as well as postsurgical states.