Three hundred and fifty four(354) cases of acute toxic encephalophalopathy including 115 cases of Reye's syndrome were admitted to the six University Hospital in seoul, Korea. From Jan. 1, 1972 to Dec. 1978. Who were clinically analyzed and following results were obtained. 1) Acute toxic encephalopathy(T.E) and Reye's syndrome(R.S) are not rare disorders but increasing tendency. 2) The peak age incidence was between 10 months and 3 years of age with 78.2% in Reye's syndrome. 3) The sex incidence revealed male predominence sligtly with sex ratio 1.16:1(M:F) in Reye's syndrome and 1.3:1 in Toxicl encephalopathy. 4) The chief compaints on admission were CNS symptoms(lethargy, delirium seizure, coma), vomiting, fever and dyspnea. 5) Major prodromal symptoms were URI and diarrhea in most cases of Reye's syndrome(82%). 6)Biochemical laboratory findings were as follow: 92% of Reye's syndrome showed elevated (more than 125mg%) GPT level. 74% of Reye's syndrome showed elevated (more than 100mg%) ammonia level. Low blood sugar(F.B.S) level were noted in 92% of Reye's syndrome 7) The prognosis and outcome were depend upon stage of coma, level of blood ammonia(more than 300ug%) and F.B.S(less than 40mg%) in Reye's syndrome. Mortality or fatality rate during hospitalization was 67.8%, only 17% of the inpatients were cured. 8) The bacterial culture were positive in 3 case of Reye's syndrome and one case of salmomella cholerasuis and 2 cases of S.flexneri were identified on blood and stool colture respectively. 9) Treatment was supportive neasure with administration of hypertonic glucose and steroid, in some cases fresh blood transfusion was added.