In this paper, we present available central nervous system data from our series of patients with the Apert syndrome. Combining our own data with that available in the literature, 30 patients had malformations of the corpus callosum, the limbic structures, or both. Other frequent findings included megalencephaly (7 cases), gyral abnormalities (8 cases), encephalocele (4 cases), pyramidal tract abnormalities (2 cases), hypoplasia of cerebral white matter (4 cases), and heterotopic gray matter (2 cases). Progressive hydrocephalus seems to be uncommon and has frequently been confused with nonprogressive ventriculomegaly in the past. Psychometric evaluations, neurological findings, and neuropathologic reports from the literature are critically reviewed. It is clear that a significant number of patients with the Apert syndrome are mentally retarded. It is suggested that malformations of the central nervous system may be responsible for most cases.