A comparative study evaluated the efficiency and safety of a novel flexible ureteral access sheath (f-UAS) versus traditional ureteral access sheath (UAS) during retrograde intrarenal surgery (RIRS) for renal stones. The study included 152 patients in each group, matched by age and stone size. The f-UAS, with a 10-cm flexible tip, allows it to follow the bends of a flexible ureteroscope (f-URS), improving maneuverability. Results showed that the f-UAS group had significantly higher stone-free rate (SFR) at 1 day postoperatively (76.3% vs. 7.2%), higher stone volume clearance (98.11% vs. 91.78%), shorter operative times (56.5 min vs. 59.9 min), lower complication rates (9.9% vs. 22.4%), and lower basket usage (17.1% vs. 100%). There was no significant difference in SFR at 1 month postoperatively or in hospital stay duration between the groups. The f-UAS demonstrated advantages in SFR, operative time, complications, and basket use. The study concluded that the f-UAS is more effective and safer than traditional UAS in RIRS, reducing complications and improving outcomes. The study also noted that the f-UAS can better navigate the ureteral anatomy, reducing the risk of mucosal injury and IRP-related complications. However, the study had limitations, including its retrospective design and single-center location. Further research is needed to confirm these findings. The f-UAS may offer a promising alternative to traditional UAS in RIRS, potentially reducing costs and improving patient outcomes.A comparative study evaluated the efficiency and safety of a novel flexible ureteral access sheath (f-UAS) versus traditional ureteral access sheath (UAS) during retrograde intrarenal surgery (RIRS) for renal stones. The study included 152 patients in each group, matched by age and stone size. The f-UAS, with a 10-cm flexible tip, allows it to follow the bends of a flexible ureteroscope (f-URS), improving maneuverability. Results showed that the f-UAS group had significantly higher stone-free rate (SFR) at 1 day postoperatively (76.3% vs. 7.2%), higher stone volume clearance (98.11% vs. 91.78%), shorter operative times (56.5 min vs. 59.9 min), lower complication rates (9.9% vs. 22.4%), and lower basket usage (17.1% vs. 100%). There was no significant difference in SFR at 1 month postoperatively or in hospital stay duration between the groups. The f-UAS demonstrated advantages in SFR, operative time, complications, and basket use. The study concluded that the f-UAS is more effective and safer than traditional UAS in RIRS, reducing complications and improving outcomes. The study also noted that the f-UAS can better navigate the ureteral anatomy, reducing the risk of mucosal injury and IRP-related complications. However, the study had limitations, including its retrospective design and single-center location. Further research is needed to confirm these findings. The f-UAS may offer a promising alternative to traditional UAS in RIRS, potentially reducing costs and improving patient outcomes.