Isolated internal iliac aneurysms are rare, and although most are of atherosclerotic origin the cause may also be congenital, traumatic, associated with pregnancy or infectious. A 56-year-old man presented with a swollen, painful left lower limb. Within a few days, weakness of the limb developed with fever and an acute abdomen with free air on x-ray. At emergency laparotomy a small perforation was found in the ascending colon. Examination of the left iliac fossa revealed a ruptured left internal iliac artery aneurysm. Extra-anatomic cross-femoral bypass grafting was done to revascularize the left lower extremity. The patient recovered without complication. At discharge the weakness had improved but knee flexion and extension were weak. Culture of the aneurysm contents grew Staphylococcus aureus and Pseudomonas aeruginosa. The authors discuss the presentation and management of infected internal iliac artery aneurysms.