Uniform neuropathological changes are described in eight cases of the progressive encephalopathy syndrome with edema, hypsarrhythmia and optic atrophy (PEHO syndrome). Two of the autopsied patients were sisters and two other cases were familial. Macroscopically, cerebral and pronounced cerebellar atrophy was seen, the essential histopathological lesions being confined to the cerebellar cortex and the optic nerve. There was a severe neuronal loss in the inner granular layer of the cerebellum. The Purkinje cells were relatively preserved in number although reduced in size, deformed and slightly disaligned. Their dendrites were horizontally oriented and the proximal axons contained abundant torpedoes. The molecular layer was narrow. The optic nerves were atrophic. Serial neuroimaging studies showed that the disease process is operative during the postnatal period, although a prenatal onset cannot be excluded. An aberrant expression of immunoreactivity against the 200-kDa neurofilament polypeptide in Purkinje cell perikarya indicated disorganization of the cytoskeleton of these cells. The combination of clinical and pathological features of our patients differs from that observed in the few published cases of so-called primary degeneration of the granular layer. Infantile cerebello-optic atrophy, clinically characterized by seizures, blindness and early arrest in psychomotor development, thus seems to constitute a new autosomal recessive disorder.