Mediastinitis due to graft infection is a serious and potentially lethal complication associated with replacement of the ascending aorta. We present the case of a 67-year-old man with this condition for the aneurysm and chronic dissection. Mediastinitis and sepsis were diagnosed and debridement, irrigation with povidone solution and omental transposition were performed successfully. Continuous closed irrigation prior to omental transposition without replacement of the infected graft is useful for treating mediastinitis after ascending aortic or arch replacement.