A case is presented of spontaneous rupture of an ileal orthotopic neobladder due to a large residual urine volume. The present case is the 13th such case reported; however, this case is the first to show lower abdominal phlegmon and in which the perforation site was detected using computed tomography scanning. The indications for neobladder should be considered with great care. If spontaneous rupture is suspected, an early diagnosis of the perforation site and a measure of the extravasation volume using computed tomography are necessary. Appropriate treatment should include laparotomy.