ObjectivesThis study evaluated the efficacy of an ultra-low-dose 0.005 % estriol vaginal gel in the prevention of urinary tract infections in postmenopausal women with genitourinary syndrome of menopause. Study designRandomized, double-blind, placebo-controlled, multicenter clinical trial conducted across 28 Spanish sites involving specialists in gynecology, urology, and primary care. A total of 108 postmenopausal women were randomly assigned in a 1:1 ratio to receive 1 g of vaginal gel with 50 micrograms of estriol or an identical moisturizing vaginal gel without estriol. Main outcome measuresThe primary outcome was the number of episodes of urinary tract infection by the end of the 24-week treatment. Secondary measures encompassed percentage of patients without recurrence, time to first recurrence, use of antibiotic treatment, vaginal pH, safety, and tolerability, among others. ResultsThe incidence rate of urinary tract infections (new cases per 100 women-year) was 26 % lower in the group that received estriol vs. the group that received placebo (32.34 vs. 43.76 (RR = 0.74) p < 0.001). The frequency of urinary tract infections fell during treatment in all patients in the estriol group. Favorable pH changes from baseline were observed in the estriol arm at all follow-up visits. ConclusionsUltra-low-dose 0.005 % estriol vaginal gel is safe and effective in preventing recurrent urinary tract infections in postmenopausal women with genitourinary syndrome of menopause, reducing the incidence and potentially decreasing the susceptibility to urogenital infections by improving vaginal pH.Study registration N°: 2018-001481-42. Date of registration: 09-04-2018.