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The clinical and pathological features of three hitherto unreported and 16 previously reported examples of clear cell adenocarcinoma of the urinary bladder and urethra are presented. Six tumors arose in the bladder and 13 in the urethra. Sixteen of the patients were female; they ranged in age from 35 to 78 years. The majority of the tumors were papillary but some were sessile. Microscopic examination revealed a variety of patterns, including tubular glands, cysts, papillae, and diffuse areas. Cells with abundant glycogen-rich clear cytoplasm and hobnail cells were identified in most of the tumors.These tumors must be distinguished from nephrogenic adenomas. A young age or a history of genitourinary trauma, operation, or calculous disease may be a clue to the latter diagnosis; microscopic features such as sheets of clear cells, significant pleomorphism, or mitotic activity favor the diagnosis of clear cell adenocarcinoma. Follow-up of most of the patients, the majority of whom were treated by a radical operation, was short; five tumors are known to have metastasized.