A 67-year-old man developed an abdominal aortic aneurysm (AAA) and Stanford type B acute aortic dissection. He received liberal antihypertensives for complicated spinal cord ischemia and, subsequently, experienced loss of appetite, followed by vomiting without abdominal pain. Computed tomography revealed AAA expansion and compression of the duodenum between the superior mesenteric artery (SMA) and AAA. He was diagnosed with aneurysmal SMA syndrome. Gastrointestinal symptoms in patients with an AAA can be a warning sign of SMA syndrome due to aortic aneurysm expansion, which can progress within a short time with accompanying acute aortic dissection.