A 59-year-old man visited another hospital with a chief complaint of malaise. Radiological examinations revealed a renal cell carcinoma associated with horseshoe kidney. He was referred to our hospital. The patient was successfully treated with open partial nephrectomy following isthmus division. Histological findings exhibited grade 2, pT1a, clear cell type, renal cell carcinoma. He is free of disease at twelve months after the operation.