To evaluate the possible effect of urinary tract infection (UTI) on the fragility of calcium-containing stones (calcium-oxalate, calcium-phosphate), the results of extracorporeal shock wave lithotripsy (ESWL) therapy in 81 patients with UTI and 30 patients with no sign of UTI were comparatively evaluated. ESWL parameters (shock wave number, kilovolt value, treatment time) and stone-free status during 3 and 6 months of follow-up were assessed for each patient, and the results were evaluated with respect to stone presence. Our results indicated that the presence of UTI may decrease stone fragility and increase stone clearance time. We believe that deterioration of peristaltic dynamics in the renal pelvis and the ureteral wall may reveal prolonged stone clearance phases in such patients.