Horseshoe kidney is the most common renal fusion anomaly found in about 0.15% to 0.25% of the population. Renal cell carcinoma associated with a horseshoe kidney has been described in fewer than 200 cases. Its incidence and prognosis seems to be not different from those of the general population, but surgical management may be challenging due to unique anatomic features of horseshoe kidneys, such as highly variable vasculature. We report a case of a 69-year-old male with an incidental 48-mm solid mass in the left moiety of a horseshoe kidney, successfully treated by retroperitoneoscopic partial nephrectomy.