This is a clinical study of 33 cases of Reye's syndrome hospitalized at Yonsei Medical Cetner from 1971 through Jun 1976. We observed following results; 1) Among the 33 cases, 6 were diagnosed by liver biopsy, 5 by autopsy and the rest 22 were diagnosed by clinical features and laboratory finding. 2) The sex ratio of male to female was 1.4:1. The majority of patients were under 2 years of age. The yearly incidence was increasing year by year and the seasonal prevalences was from late spring through to fall. 3) The common abnormal clinical features were analyzed ; seizure was noticed in all cases and vomiting, tachypnea, hepatomegaly were noticed in two third of patients. 4) The common abnormal laboratory findings were consisted follow blood sugar below 80mg/dl, SGOT above 40 units, prolongation of prothrombin time longer than fourteen seconds was noticed in 90% of patients. And low CSF sugar level below 40mg/dl was noticed in 90% of patients. In pathologic examination, not only the liver but kidney and brain showed fatty infiltration. 5) The outcome of these patients according to Huttenlocher's classification is getting worse according to the progression of the disease; in stage I two cases were survived without a death, stage II one died in seven, eleven died in fifteen cases of stage III and stage IV nine cases died without survival. Of all motality rate was 63.6%.