Objective: To analyze the predictive factors for intraoperative ureteral wall injury due to semirigid ureteroscopy (URS) used in the treatment of ureteral calculi. Methods: The data of 437 patients who had URS due to ureteral stones were prospectively analyzed. The ureteral wall injuries that occurred during URS were reviewed endoscopically at the end of surgery and divided into two groups as low grade (grades 0 and 1) and high grade (grades 2, 3, and 4) according to classification of ureteral wall injuries. Those two groups were compared for patient and stone characteristics and perioperative findings. Results: Ureteral wall injury was seen in 133 (30.4%) patients after surgery. According to the endoscopic classification of the lesions after URS, grades 0, 1, 2, and 3 injury were seen in 69.5%, 16.4%, 11.2%, and 2.7% of the patients, respectively. There were no grade 4 injuries in our series. Two groups showed statistically significant differences for the location (prox- vs distal and mid-ureter) and size of the stone (9.9mm vs 14.03mm), presence of preoperatively urinary tract infection (UTI) (12% vs 50.8%), needed balloon dilatation (9.8% vs 36.1%), duration of surgery (33.6min vs 43.3min), and surgical success rate (90% vs 76%) (p=0.01, for all). Stone size, location, duration of surgery, and presence of preoperative infection were determined as independent prognostic factors for mucosal injury. Conclusion: The ureteral wall injury grading system may be used for standardized reporting of ureteral lesions after ureteroscopy. Big, proximal ureteral stone, longer operation time, and presence of UTI are the risk factors for ureteral wall injury during URS.