A family with the clinical features of Behr's syndrome is described that exhibited probable pseudodominant inheritance. The salient clinical manifestations consisted of mental retardation and dementia, optic atrophy, cerebellar ataxia, pyramidal signs and peripheral neuropathy. Nerve biopsy from the index case showed a chronic neuropathy with axonal degeneration and regeneration. A muscle biopsy from the same patient demonstrated multiple inclusions composed of spiral cylindrical structures possibly derived from the sarcoplasmic reticulum, and less obtrusive accumulations of mitochondria, some of which contained paracrystalline inclusions.