Objectives: Assessement of the causes of failures in ureteroscopic lithotripsy. Material and Methods: From August 2006 to April 2013, in Hue Centrel Hospital, the authors treated 1276 patients (1330 ureters) with ureteral calculi by ureteroscopic lithotripsy. Results: The success of ureteroscopy assess to the stones is 97.89 percent, failure is 2.11 percent. The success rate of lithotripsy is 92.55 percent, failure is 7.45 percent (for stones of 1/3 upper ureter 4.66 percent, and 1/3 lower ureter 2.79 percent). Failure rate using Laser is 1.83 percent (stones move into the kidney). Failure rate using pneumatic lithobipsy is 24.52 percent. Conclusions: ureteroscopic lithotripsy is a safe, effective, less traumatic method. The causes of failure are mainly high position, and big size of stones, severe hydronephrosis. The big advantage of the laser is able to break all kinds of stones.