A 55-year-old man with a huge cystic lesion in the left kidney was referred to our department. Preoperative computed tomographic scan with enhancement by contrast agents showed that the cyst wall had solid components. Left radical nephrectomy was performed. The resected kidney with giant hydronephrosis weighed 3,950 g and had a ureteral stone with a long diameter of 27 mm. The tumor had infiltrated the renal pelvis, and it was unclear whether the tumor had originated from the kidney or pelvis. Pathological findings showed that the tumor was sarcomatoid renal cell carcinoma. He was started on IFNa and IL-2 therapy. However, brain metastasis soon appeared followed by general worsening of his condition, and he died a month after the surgery.