A 9-month-old male infant was admitted to our hospital on the second day of cold like syndrome because of high fever, convulsion, coma, and decerebrate rigidity. Serum GOT, GPT, LDH, and CPK were markedly elevated. Serum ammonia was slightly increased, and hypoglycemia was present. The cerebrospinal fluid showed no pleocytosis, normal sugar content, but increased protein. Thus we made a diagnosis of clinical Reye syndrome according to the criteria by Yamashita, et al. A CT on the day of admission showed symmetrical low-density areas in the posterior fossa and the regions of thalamus. Ringed enhancements were seen around the areas of low density in the thalamus on the twenty-second hospital day. We consider that these lesions may represent the infarction due to obstruction of the thalamoperforant arteries caused by cerebral edema in the early stage of the disease.