OBJECTIVETo compare intraoperative ureteral injuries in RIRS with UAS insertion with the rate of postoperative infections after RIRS without UAS insertion.PATIENTS AND METHODSIn this randomized trial, patients who received an indication for RIRS between January 2017 and December 2017 were divided into two groups. Group A had no UAS insertion and Group B had UAS insertion. Post-Ureteroscopic Lesion Scale (PULS) grading was performed after UAS or flexible ureteroscope removal. Proximal, middle and distal ureteral lesions were evaluated and compared according to the PULS scale. Additionally, patients in both groups were followed postoperatively to assess any infective complication.RESULTSThe evaluation comprised 181 patients, 89 for group A and 92 for group B. Overall stone-free rate, clinically insignificant residual fragments, and final stone-free rate were 41.4%, 53.5%, and 95%, respectively. There were 33 (37.1%) patients with ureteral lesions in group A while 42 (45.6%) patients had ureteral lesions in group B, with no significant difference. On the other hand, the overall presence of postoperative infection rate was much higher for Group A (37.1% vs 16.3% P=.03).CONCLUSIONSUAS insertion does not result in a higher number of ureteral injuries. UAS insertion during RIRS allows a lower rate of postoperative infections. Clinical Trial Registration Number (ISRCTN registry number): 55546280.