A 68-year-old man presented with a chief complaint of left leg pain; he was later diagnosed with an infected left internal iliac artery aneurysm. Multiple mononeuropathy was suspected. Since the aneurysm had a high risk of rupture, emergency Y-graft replacement was performed. Bacteroides vulgatus was then detected from the pus of the aneurysm. With continuous oral antimicrobial agents following intravenous antimicrobial agents, the patient was noted to have no recurrence. However, his leg pain symptoms continued postoperatively; thus, a supporting device was needed. It should be noted that even neurological symptoms may indicate the presence of aortoiliac aneurysms.