A family--mother and 2 sons--with a heredodegenerative neurological disease is described. The disease started with bilateral optic atrophy, central scotoma, and color blindness during the second decade. This was followed by a quiescent period until additional neurological symptoms appeared, around the age of 50 years in the case of the mother and 40 and 30 years, respectively, in the sons. The additional symptoms were ataxia, spastic paresis, clonic jerks, grand mal seizures, psychia lability, and slight dementia. The disease was progressive, resulting in permanent hospitalization within a few years. The mother died at the age of 63 years and the sons at 46 and 43 years of age. Neuropathological examination revealed lesions histopathologically characteristic of subacute necrotizing encephalomyelopathy (SNE, Leigh disease), and their distribution in the brain and brainstem also conformed to this disease. On the basis of the clinical course and neuropathological findings, we consider that these 3 patients represent the first reported familial cases of the adult form of SNE.