Ligation of the internal iliac artery mostly remains without consequences because of the well established collateral network. In patients with compromised collateral circulation however, acute interruption of both hypogastric arteries during aorto-iliac surgery or transluminal embolisation can lead to necrosis of the gluteal muscles and other adjacent organs (rectum, bladder, lumbosacral plexus). Experience with 3 similar cases after aorto-iliac surgery demonstrates two main intraoperative mechanisms: 1. Embolisation, 2. Ligature of both internal iliac arteries in patients with compromised arteriosclerotic collaterals. Despite of adequate therapy, mortality is over 70%. The most important feature during aorto-iliac operations is to preserve at least one internal iliac artery by either reimplantation of the main stem or by an additional bypass to this artery.