Gastrointestinal complications (GI) after thoracoabdominal aortic repair can be classified as biliary disease, heptic dysfunction, pancreatitis, GI bleeding, peptic ulcer disease, bowel ischemia, paralytic ileus, and aortoenteric fistula. Theses complications are associated with high post operative morbidity and mortality. Most of the aortoenteric fistulae after thoracoabdominal aortic surgery are found at the duodenum, near the surgical site. These rare complications are caused by an indirect communication with abdominal aorta that originated from an aneursymal formation ruptured into the duodenum. Such aorto-duodenal fistula formation is considered as a result of inflammatory change from secondary infection near the surgical instruments. Herein, we report two cases of massive upper GI bleeding from aorto-duodenal fistulae and spontaneous lower GI perforation related to cytomegalovirus infection after abdominal aortic aneurysmal repair operations. (Korean J Gastroenterol 2010;55:62-67)