Carcinoma of the urachus, which is a rare entity with poor prognosis, had proved difficult to diagnose radiographically. Since urachal carcinomas develop primarily in or outside the blader, with invasion of the mucous membrane occuring later, the tumor is likely evade dtection until it is too late. However, with the advent of computed tomography, the anatomical relationship of a mass to the bladder can be better demonstarted and the diagnosis suggested. The purpose of this presentation is to describe a case of the urachal carcinoma and to show the usefulness of CT in the diagnosis and follow up.