INTRODUCTION AND OBJECTIVE: Ureteroscopy (URS) procedure duration has been associated with complications such as ureteral perforation and urosepsis, as well as higher costs. A new FDA approved lithotripter, the thulium fiber laser (TFL), was made commercially available in June of 2020 and was acquired by our institution. This retrospective study was designed to determine if TFL lithotripsy decreased operative time when compared to standard Holmium:YAG (Hol:YAG) lithotripsy without pulse modulation. METHODS: A retrospective review of URS with laser lithotripsy at a tertiary stone center was conducted for cases performed 2 months before and 2 months after conversion to TFL lasers for URS. 152 procedures were identified. Cases that involved bilateral procedures, aberrant anatomy, had no recorded kidney stone composition, and those that were aborted due to complications or tight ureters were excluded from analysis. 102 cases met inclusion criteria, 51 in each arm. Operative time was measured from scope in to scope out. Variables including stone size, location, chemical composition, prior ureteral stenting and ureteral access sheath use were recorded. In cases with 2 or more stones, the cumulative stone diameter was measured from preop CT imaging and reported as the summation of diameters from all treated stones. RESULTS: Baseline characteristics of the patients and stones treated did not differ significantly between laser groups (table 1). Compared to Hol:YAG, use of TFL resulted in an average decrease of 12.94 minutes per case (p=.021, 95% CI [2.03-23.85]). In subgroup analysis of cases with cumulative stone diameter less than 15mm, the difference was 13.95 minutes (p=.007, CI [3.95-23.95]). For cases less than 10mm, the mean difference was 17.27 minutes in favor of TFL (p=.002, 95% CI [6.89-27.62]). Stone free states confirmed by retroperitoneal ultrasound were similar between groups but could not be reliably estimated due to low (36%) compliance with post op imaging in the COVID era. CONCLUSIONS: TFL is a substantially faster means of laser lithotripsy than Hol:YAG with average case time reduced by 20% overall (13 min). As the number of URS laser lithotripsy procedures being performed in the United States continues to increase, reducing procedure times has the potential to improve patient outcomes and decrease costs. Longer term follow up is needed to see if recurrence rates are affected.