A 41-year-old man with macroscopic hematuria and abdominal fullness was referred to our hospital. Computed tomography (CT) revealed a left renal pelvic tumor in the horseshoe kidney. We performed left heminephrectomy and ureterectomy. The pathological diagnosis was the mucinous adenocarcinoma in the renal pelvis. He received postoperative adjuvant chemotherapy (CAP therapy). He died of retroperitoneal recurrence 8 months postoperatively. In the literature we found 95 cases of primary adenocarcinoma in the renal pelvis including our case.