A 38-year-old man underwent replacement of the ascending aorta and aortic arch for acute type A dissection. On the 11th postoperative day he developed mediastinitis. Omental transposition was performed successfully. The patient was readmitted for bloody discharge from the wound. He suffered from back pain suddenly. Computed tomography and aortography revealed an anastomotic pseudoaneurysm of the ascending aorta. Emergency reoperation to replace the ascending aorta with a new prosthesis was performed. The postoperative course was uneventful.