Importance There is little consensus on an effective nonantibiotic agent for the prevention of urinary tract infection (UTI) after pelvic reconstructive surgery. Objective The aim of the study was to investigate the impact of methenamine hippurate with cranberry capsules on rates of UTI after pelvic reconstructive surgery, among patients requiring short-term catheterization. Study Design In this randomized, double-blinded placebo-controlled trial, patients discharged with a catheter after pelvic reconstructive surgery were approached to participate. Participants were randomized to receive cranberry with methenamine or cranberry with placebo. Primary outcome was number of UTIs treated within 1 week after surgery. Secondary outcomes included incidence of UTIs treated within 6 weeks postoperatively, bacterial species on culture, urinary pH, catheter duration, patient adherence, and satisfaction. A sample size of 88 participants per arm was planned. Results From June 2019 to July 2021, 185 patients were randomized and 182 analyzed; 89 received placebo and 93 received methenamine. Both groups were similar. Incidence of UTI at 1 week was significantly higher in the placebo group (79.8%) compared with the methenamine group (66.7%; odds ratio, 1.97; 95% confidence interval, 1.01-3.87; P = 0.048). This difference increased by 6 weeks postoperatively (89.9% vs 72.0%; odds ratio, 3.45; 95% confidence interval, 1.51-7.87; P = 0.003). There were fewer pseudomonal UTIs in the methenamine group (P = 0.041). Duration of catheterization and urinary pH were similar. Overall adherence and level of satisfaction was high. Conclusions In this high-risk population, methenamine was well tolerated and significantly reduced UTI rates. Methenamine with cranberry should be considered as an effective prophylactic therapy to reduce this common complication after pelvic surgery.