We report a case of renal cell carcinoma in a horseshoe kidney in a 48-year-old man. A medical checkup revealed a renal tumor in the right kidney. Computed tomographic scan (CT) showed a renal tumor measuring about 4 cm in diameter on the right side of a horseshoe kidney. Right heminephrectomy was performed for renal cell carcinoma. Pathologic examination revealed renal cell carcinoma, clear cell subtype, G1>G2, INF alpha, pT3a, V (-). In addition to our case, we review 66 cases of renal cell carcinoma occurring in a horseshoe kidney which have been reported in Japanese publications; our case is the 67th.