Isolated iliac artery aneurysms are uncommon. Current recommendations favor elective repair in aneurysms measuring more than 35 mm in healthy patients. We describe here a ruptured isolated common iliac artery aneurysm with a maximum diameter of 22 mm. A 79-year-old man was transferred to our hospital in a shock state. Contrast media enhanced computed tomography scan revealed a ruptured isolated left common iliac artery aneurysm with a maximum diameter of 22 mm. Emergency open repair was carried out. Localized arterial dissection was found at the proximal wall of the ruptured site. It seemed rare that the rupture of iliac artery aneurysm occurred with such a small diameter.