A case of neuronal intranuclear hyaline inclusion disease (NIHID) is described, and the literature on seven reported cases is briefly reviewed. The patient was a 24-year-old man who died of a chronic progressive neurologic disease starting at the age of 6 years. Clinically, the disease presented as Friedreichs's ataxia, and pathologically it was characterized by multisystem atrophy. An outstanding feature was the presence of widespread intranuclear hyaline inclusions in neurons of the brain, spinal cord, and myenteric plexus of the gut. The inclusions displayed yellow-green autofluorescence under ultraviolet (UV) light and were filamentous ultrastructurally. It seems that cases bearing such peculiar neuronal inclusions represent a distinct disease entity of unknown origin. The disease, which is sometimes familial, usually starts in childhood and affects both sexes. Clinically, it presents as multisystem degeneration with progressive ataxia as the prominent feature. Pathologically, it is characterized by neuronal loss, fiber tract atrophy, and intranuclear neuronal inclusions. In some cases such inclusions were found also in neurons of the myenteric plexus. Since these are accessible to biopsy it is recommended that rectal biopsy be made in every case of "atypical" system atrophy.