Objectives: To assess efficacy and safety of Bio-Kult Pro-Cyan (BKPro-Cyan), a product containing two strains of Lactobacilli plus cranberry extract, for preventing recurrent UTIs in pre-menopausal adult women. Methods: This was a randomized, double-blind, placebo-controlled pilot study. Subjects received BKPro-Cyan or placebo twice-daily for 26 weeks. The primary endpoint was the proportion of subjects with recurrent UTI at the end of the study. Results: 115 subjects were screened; 90 were enrolled; 81 completed the study. After 26 weeks, a significantly lower number of women experienced recurrent UTIs with BKPro-Cyan compared to placebo (9.1 vs 33.3%; P=0.0053). BKPro-Cyan produced statistically significant improvements compared to placebo for multiple secondary endpoints, including: greater number of subjects who experienced no UTIs (90 vs 67%; P<0.05); longer time to first UTI (174 vs 90 days; P=0.001); shorter duration of active UTI (5 vs 12 days; P=0.009); Fewer subjects requiring antibiotics (3 vs 11; P<0.05); and shorter median duration of antibiotic treatment (4 vs 7 days; P=0.09). Conclusions: BKPro-Cyan was safe and effective for preventing recurrent UTI in pre-menopausal adult women. These findings support the need for further well-designed trials to clarify the benefits that may be achieved.