Urachal carcinoma arises in the clinically silent extraperitoneal space between the bladder apex and the umbilicus. Computed tomography was used to correctly diagnose and stage urachal cancer in two patients. In one case a mass was localized to the bladder wall and immediate juxtavesical region; in the other case an advanced locally invasive lesion was seen to engulf and fisulize loops of small bowel and extend through the umbilicus. Urachal carcinoma has a highly characteristic appearance and location on CT images.