Three cases of malignant tumor metastasis to primary renal cell carcinoma (RCC) are described. We review the literature on this subject and emphasize the possible mechanisms of this observation in 46 patients described in the English literature. RCC is the most common tumor recipient of metastasis while carcinoma of the bronchus is most consistently the metastatic donor. This phenomenon is not as infrequent as previously thought and may be present in up to 15 per cent of patients with simultaneous RCC and second neoplastic disease.