Clinical and Pathological findings of the third Japanese case of subacute necrotizing encephalopathy has been reported. The patient was a 6-year-old girl at death. In family history her elder brother sffered from an illness with symptoms similar to those of her, and died at the age of 71/2 years. About a year prior to death she began successively to have symptoms including dyspnoeic fits, disturbances in gait and in speech, divergent strabismus, nystagmus and tremor of fingers. The symptoms progressed gradually, and she died of dyspnoea which happened during procedure of a pneumoencephalography. Neuropathologically the necrotic lesion with vascular proliferation was found in the striatum, pontine tegmentum and medulla oblongata. No change was found in the substantia nigra and mamillary bodies. In discussion problems of differential diagnosis between the disease and Wernicke's encephalopathy were considered with quating literature. The pathogenetic problems of the disease were also discussed.