A 79-year-old woman was evaluated for a ureteral stricture related to laser ablation of a tumor 6 months earlier at another institution. A ureteroscopic examination revealed an exophytic papillary tumor that was resected and examined histologically. The tumor was characterized by delicate papillae with thin stromal cores and numerous secondary micropapillae lined by small cuboidal to low columnar cells with uniform low-to-intermediate-grade nuclei, reminiscent of a serous borderline tumor of müllerian origin. The cell linings were 1 to 4 layers thick; mitotic figures were easily identified. The underlying stroma appeared edematous and contained scattered chronic inflammatory cells. No invasion was identified. After ascertaining that the patient had no known gynecologic neoplasm, the differential diagnoses considered included papillary nephrogenic adenoma, clear cell carcinoma, and the recently described entity of micropapillary transitional cell carcinoma. Because of the striking resemblance to serous carcinoma and the presence of significant mitotic activity, this case was felt to represent a case of micropapillary transitional cell carcinoma (World Health Organization grade 1 to 2) occurring in the ureter. To our knowledge, this tumor had some unique features (no areas of grade 3 nuclei or invasion) that have not been reported in tumors occurring in the urinary bladder. The transitional cell nature of the tumor cells was supported by the immunohistochemical staining pattern. The anatomic distribution of micropapillary transitional cell carcinoma is now expanded to include the ureter, and this tumor should be considered in the differential diagnosis for papillary lesions occurring in the ureter.