Renal oncocytoma is a neoplasm which rarely occurs in patients with solitary kidney, the other being absent because of a previous nephrectomy performed for renal cancer. We present two case reports and a literature review. We have studied some important problems such as the histogenesis, the potential for malignancy, the diagnosis, the treatment and the follow up. The high incidence of coexistence of renal oncocytoma and renal cell carcinoma has important clinical implications. We would like to emphasize the importance of preoperatory FNAB, nephron sparing surgery and very careful follow up.