The stone-free rate after extracorporeal shock wave lithotripsy (ESWL) is primarily determined by a plain abdominal radiograph alone. However, the accuracy of that assessment can be challenged by renal tomography and flexible nephroscopy. We report on 29 patients with large renal calculi treated with a combination of percutaneous nephrolithotripsy and ESWL. Stone-free rates were determined by plain abdominal radiograph, renal tomography and flexible nephroscopy. The plain abdominal radiograph and renal tomography overestimated stone-free rates by 35% and 17%, respectively, compared to flexible nephroscopy. To determine stone-free rates after ESWL renal tomography is superior to a plain abdominal radiograph alone. Also, among patients with large renal calculi the use of the flexible nephroscope markedly improves the stone-free rate.