A 5-year-old girl with a history of recurrent urinary tract infection since the age of 14 months was diagnosed as having a right duplicated urinary collecting system with the upper ureter ectopically opening in the urethra. She underwent retroperitoneoscopic heminephrectomy for a right dysplastic kidney and open ureterocelectomy and reimplantation of the refluxing lower ureter via Pfannenstiel incision. She survived the procedure without serious complications and resumed normal daily activities by day 6. To the best of our knowledge, this case is the 16th case of laparoscopic heminephrectomy for pediatric patients and the first case treated by the retroperitoneal approach in the English literature.