Fankhauser CD, et al. - The efficacy and safety of extracorporeal shock wave lithotripsy (ESWL) and flexible ureterorenoscopy (URS) were compared for previously untreated renal calculi. Stone size and treatment modality were the factors on which treatment success was mainly dependent. For previously untreated kidney stones 5-20 mm, URS could be the better treatment option with similar morbidity but higher stone-free rates and fewer reinterventions than ESWL.