Primary small-cell carcinomas of the kidney are rare, locally aggressive, and rapidly fatal neoplasms in elderly people. We report an example of combined small-cell and transitional cell carcinoma of the renal pelvis in a 71-year-old woman who had a history of heavy smoking. The cells that pertained to the small-cell component were morphologically mostly of an intermediate type. Immunohistochemically, they reacted with synaptophysin, carcinoembryonic antigen, and epithelial markers (Lu-5, EAB902, EAB903, and cytokeratin 19), and they contained scanty neurosecretory granules at the ultrastructural level. We review the literature on small-cell carcinoma of the kidney and renal pelvis, and we discuss the histogenesis of such a tumor.