An 8-year-old girl and her 4-year-old sister presented with psychomotor retardation during the 1st year of life. This was followed by spasticity, seizures, and in the older patient, progressive loss of faculties and death. Computed tomographic and magnetic resonance imaging scans demonstrated progressive cerebral atrophy in both patients. Postmortem examination in the older sibling showed diffuse atrophy of the supragranular layers of the cerebral cortex, atrophy and gliosis of the white matter, and accumulation of numerous amylaceous (polyglucosan) bodies within the cytoplasm of cell processes. The inclusions were closely associated with atrophy of the parenchyma. The findings suggest that this disorder is different from other childhood diseases in which amylaceous bodies accumulate within the brain.