In 1980, Fukuhara et al. have reported two patients with "myoclonus epilepsy associated with ragged-red fibers" (MERRF), which is at present accepted as a distinctive clinical entity among the mitochondrial encephalomyopathies. We describe here postmortem findings of the case whose clinical findings were reported in detail by Fukuhara et al. (1980) as Case 1. The neuropathological findings were summarized as follows: 1) degeneration of dentate nucleus, red nucleus, globus pallidus, subthalamic nucleus and pontine tegmentum, 2) degeneration of the Clarke's column, spinocerebellar tract, posterior column and corticospinal tract, as well as of the posterior spinal nerve root and sural nerve, and 3) degeneration of substantia nigra, locus ceruleus, cerebellar cortex and inferior olivary nucleus. The lesions were degenerative in nature, and their distribution was different from those of dentato-rubropallidoluysian atrophy, Joseph's disease or Friedreich's ataxia. It was concluded that MERRF is a single disease entity also from pathological point of view.