The computed tomographic (CT) appearance of urachal carcinoma in ten patients was studied and compared with the pathologic findings. Magnetic resonance images were available in one case. All tumors were mucinous adenocarcinomas; four were solid, three were cystic, and three were mixed. The tumor had a characteristic location along the expected midline course of the urachus directly behind the anterior abdominal wall. The main tumor mass was supravesical in eight patients. Seven tumors contained calcification. CT correctly depicted bladder wall involvement and supravesical extent of tumor in all cases. CT provided incorrect information about invasion of the perivesical fat in three patients and about bladder mucosal invasion in two patients.