The purpose of this report is to present a rare case of lumbar artery aneurysm. We report the case of a 54-years-old male patient who was misdiagnosed over years having a chronic infrarenal aortic aneurysm. A 64-slice CT at our institution revealed a large lumbar artery aneurysm. The conclusion of this case report is that a lumbar or accessory renal artery aneurysm has to be taken into consideration if there is a localized enlargement of the lower abdominal aorta and a high resolution CT-scan is strongly recommended to make the exact diagnosis.