Aims: The guidelines propose optical dilatation before retrograde intrarenal surgery (RIRS), but there are no evidence-based studies concerning the impact of optical dilatation with semirigid ureteroscopy (sURS) in the literature. The aim of this study was to evaluate the effect of optical dilatation through sURS prior to the procedure on the success and complications of RIRS. Methods: In a multicentre retrospective study, 422 patients were included in the study. The patients were divided into two groups according to whether sURS was to be performed. Patients’ demographics, stone parameters and operative outcomes were compared. Surgical success was defined as no or up to 3-mm residual stone fragments without the need for additional procedures. The independent predictors for surgical success were determined with a multivariable logistic regression model. Results: Of the 422 patients, 133 (31.5%) were in the sURS group and 289 (68.5%) were in the non-sURS group. Operation time in the sURS group was significantly long (p<0.0001). A ureteral access sheath (UAS) could not be placed in four (3.0%) patients in the sURS group, nor in 25 (8.7%) patients in the non-sURS group (p=0.03). Compared with the non-sURS group, the intraoperative complication rate was low in the sURS group (14 (4.8%) vs 1 (0.8%), p=0.04). The surgical success rate was higher in the sURS group (p=0.002). Nevertheless, sURS had no independent effect on surgical success. We have found two independent predictors for surgical success rate: stone number (p<0.0001, OR:2.28) and failed UAS placement (p=0.035, OR:3.49) Conclusion: Optical dilatation with sURS before RIRS increases surgical success by raising the rate of UAS placement and reducing the rate of intraoperative complications. We suggest that this method can be routinely applied in the group of patients who have not been passively dilated with a JJ stent