Fifty-seven patients of type A aortic dissection were underwent operations from Jan. 1985 to Nov. 1994. The number of patients who underwent graft replacement of the aorta and received aortogram after the operation was twenty-nine. To investigate factors affecting the occurrence of anastomotic leakage after graft replacement of the aorta, the aortograms of the 29 patients were examined retrospectively. The aortograms revealed leakage at the distal anastomotic site on 11 of the 29 patients. Eight factors: the kind of graft, Marfan's syndrome, the use of felt at the anastomotic site, the clamping method, distal anastomotic site, acute or chronic, the state of the aortic wall at the anastomotic site and the blood pressure control after operation, were examined relating to the occurrence of anastomotic leakage. The results showed 3 factors; acute or chronic, the state of the aortic wall and the blood pressure control, affected the occurrence of anastomotic leakage. In short, the anastomotic leakage easily occurred in patients who underwent in the acute stage and whose blood pressure was uncontrolled after the operation. Therefore, strict control of the blood pressure after the operation is the most effective for preventing anastomotic leakage.