A 72-year-old man was referred to our hospital because of lumbago and an abdominal aortic aneurysm (AAA). Computed tomography revealed the AAA to be 5cm in diameter with a retroperitoneal hematoma. A diagnosis of chronic contained rupture of an AAA was made, and an operation was performed. At laparotomy, a punched-out defect (10×20mm) that was thought to connect the thrombosed aneurysm to an organized retroperitoneal hematoma was discovered on the right side of the aorta. The aneurysm was replaced with a Y-shaped prosthetic graft. The patient's postoperative course was uneventful. This case of chronic contained rupture of an AAA was distinctly different from cases of acute rupture. Although patients with chronic contained rupture of an AAA are hemodynamically stable, such cases should be assessed and treated as quickly as possible because of the risk of re-rupture.