A retrospective study of 166 cases of cerebral infarction who were treated at the Takamatsu Red Cross Hospital from 1983 to 1986 was conducted. 1) There was no significant relationship between cases of cerebral infarction deaths and smoking, alcohol consumption, high blood cholesterol levels, high blood neutral fal levels or diabetes. 2) Those cases of cerebral infarction which were complicated by heat disease or atrial fibrillation demonstrated a significantly higher mortality rate. 3) From among a total of 20 cases of cerebral infarction complicated with heart disease, 12 cases had a simultaneous complication of atrial fibrillation. The most common type of heart disease observed was cardiac valve disease, which was present im 7 of the cases. 4) All 4 cases of cardiac infarction were not complicated by atrial fibrillation. 5) All of the cases of death due to cerebral infarction compicated by heart disease were also complicated by atrial fibrillation. These finding indicate the importance of atrial fibrillation in cases of cerebral inflarction. A study of the clinical picture of cases of cerebral infarction complicated with atrial fibmillation was conducted. 1) The clinical picture od cases of cerebral infarction complicated by atrial fibrillation frequently involed cerebral embolism and the site of infarction was frequently observed to be the dendrifrom cerebral cortex. In addition, these cases were usually quite severe, even resulting in consiousness disorders and also involved a high mortality rate. 2) In comparison to cases which were not complicated by atrial fibrillation, there was no significant difference observed between such cases nd survivors of cerebral infarction complicated by atrial fibrillaiton in terms of their function of movement and social life style. Based on the above, atrial fibrillation is believed to be a major risk factor of cerebral infarction irrespective of the presence or absence of underlying disorders.