We present a patient of a 68-year-old man with a thoracoabdominal aortic aneurysm, which make us difficult to have a diagnosis of inflammatory or infected. The rapid expansion of the aneurysm was detected on computed tomography despite steroid or antibiotic therapy. Severe adhesion was seen on the distal site of the aneurysm, but we successfully underwent graft replacement of thoracoabdominal aorta with reconstruction of visceral artery. His postoperative course was uneventful. Pathological findings showed not infected but inflammatory changes.