To share our multicenter experience using a safe and effective method for treating large proximal ure-teral calculus by simultaneous supine percutaneous nephrolithotomy (sPCNL) and retrograde ureterolithotripsy (URSL) in the Galdakao-modified supine Valdivia position. Between December 2014 and August 2017, all patients with large proximal ureteral stones (> 15 mm) who underwent simultaneous sPCNL and retrograde URSL at three medical centers were retro-spectively reported. The ureter stone was pushed back (retrograde) with the ureteroscope and was retrieved using forceps with a nephroscope through an Amplatz sheath. Surgical methods and outcomes were described to improve our experience and management of large proximal ureteral calculi. A total of 31 patients underwent simultaneous sPCNL and retrograde URSL. The mean patient age, stone size, operating time, and postoperative hospital stay were 57 years (range, 32-74 years), 20.1 mm (range, 15.0-37.9 mm), 81 minutes (range, 30-150), and 3.2 days (range, 2-7 days), respectively. There were 10 modified Clavien grade I and five grade II complications. No blood transfusions were necessary in this series. All patients were treated with double-J stents without a nephrostomy tube. Only one patient did not achieve stone-free status because of the strict stone impaction into the ureteral wall. This patient received auxiliary URSL after two months. Thereafter, the overall stone-clearance rate at three months was 100%. Our preliminary data showed that this modified method is safe and effective for treating large prox-imal ureteral stones.