Diffuse degeneration of the cerebral cortex and claustrum was found in the brain of a 7-week-old baby with profound psychomotor retardation, multiple ankyloses, seizures, and hypothalamic dysfunction. There was ubiquitous Pick cell formation and gliosis in the affected gray matter. The cortex was not atrophic; in fact, the brain was moderately enlarged. The clinical and pathological findings suggest that the disorder should be distinguished from Pick's disease, as well as from other congenital encephalopathies.