A case of a carcinoid tumor of the kidney that was intimately related to a mixed dysplastic and teratomatous lesion is reported. This lesion displayed focal transitional, mucinous, and endocrine differentiations. Immunofluorescence studies permit the identification of three immunoreactive products: somatostatin, glucagon, and serotonin. It is suggested that the carcinoid tumor arises from this peculiar lesion, which exhibits cells of endocrine lineage.