Transitional cell carcinoma is the most common malignant tumor of the urteter, usually presenting as focal ureteral wall thickening or a mass filling the ureter lumen and combined with periureteral infiltration or adjacent lymph node enlargement. Retroperitoneal mass due to exophytic growth of ureteral transitional cell carcinoma has not been described in the literature, and we now report the CT findings in such a case.