Although almost all cases of spontaneous aortic dissection originate in the thoracic aorta, dissections limited to the abdominal aorta occur very rarely. According to the previous literatures, localized abdominal aortic dissections account for 1~4% of all aortic dissections. The predisposing factors of spontaneous abdominal aortic dissection are similar to those of thoracic aortic dissection. Many patients have a history of hypertension and the incidence appears to be greater in patients with congenital heart diseases, pregnancy or Marfan's syndrome. And it occurs 3 times more frequently in men than in women. Histologically, atherosclerosis is the most common finding. In many cases, presenting symptoms and signs are not specific, so that this disease entity can be overlooked at bedsides. In our case, the patient was a 76-year-old man who had a vague periumbilical pain occurred one day before. He had no trauma history nor other illness. Abdomino-pelvic CT showed 4x7 cm sized dilatation of abdominal aorta from below the renal arteries to just above the aortic bifurcation site and compatible with aortic dissecting aneurysm. We performed aneurysmectomy and restored arterial continuity with an aorto-bifemoral bypass using dacron. The patient's postoperative course was relatively uneventful and he remains well one year after operation. In conclusion, because of its rarity and nonspecific symptoms and signs, spontaneous aortic dissection confined to the abdominal aorta may be misdiagnosed by physicians. And usually, untreated aortic dissections have a lethal course. So, more accurate diagnostic approaches and optimal managements are needed for good outcome.