We report a case of renal cell carcinoma with polymyositis. A 62-year-old female with a diagnosis of polymyositis was referred to our department because of the right renal mass discovered by computed tomography. An ultrasonography and renal angiography showed a solid and hypovascular area at the middle pole of the right kidney. A fine needle aspiration biopsy of the mass was performed and the cytology showed a papillary adenocarcinoma. Therefore, the right radical nephrectomy was carried out and her myopathic symptoms were slightly improved postoperatively. The patient has remained well without recurrence or metastasis for two years.