Clear cell adenocarcinomas of the urinary bladder are rare tumors with an unknown histogenesis. Since these tumors appear histologically similar to clear cell tumors of the female genital tract, a mullerian histogenesis has been proposed. Several publications have examined the immunohistochemical properties of clear cell adenocarcinomas to improve understanding of the cause and pathogenesis of this tumor. While specific criteria for a diagnosis of clear cell adenocarcinoma have not been defined, there are consistent staining patterns suggested for characterization. We present an important case of clear cell adenocarcinoma of the bladder with a unique staining pattern. We review the literature and discuss the differential diagnosis and various theories concerning the origin of this rare tumor.