Aneurysms of the iliac arteries usually remain silent, but when they rupture the consequences can be dramatic. They produce few clinical signs suggestive of their presence. However, such aneurysms have been found to be the cause of non-vascular clinical situations. Often they present with features of compression on adjacent viscera. We present a case in which a large common iliac artery aneurysm was found to be causing symptoms of acute sciatic nerve compression.