OBJECTIVE: To evaluate whether cranberries are able to prevent postoperative urinary bacteriuria in patients undergoing pelvic surgery and receiving transurethral catheterisation. DESIGN: Randomised, double-blind, placebo-controlled trial. SETTINGS: French tertiary Care centre, University Hospital. POPULATION: A total of 272 women undergoing pelvic surgery aged 18 or older. METHODS: Participants undergoing pelvic surgery were randomised to 36 mg cranberry (proanthocyanidins, PAC) or placebo once daily for 10 days. Statistical analysis was performed by a chi-square test. MAIN OUTCOME MEASURES: The primary and secondary outcomes were postoperative bacteriuria, defined by a positive urine culture, within the first 15 and 40 days, respectively. RESULTS: Two hundred and fifty-five participants received the intended treatment: 132 (51.8%) received PAC and 123 (48.2%) received placebo. There were no significant differences in baseline demographics, intra-operative characteristics or duration and type of catheterisation between the two groups. PAC prophylaxis did not reduce the risk of bacteriuria treatment within 15 days of surgery [27% bacteriuria with PAC compared with 25% bacteriuria with placebo: relative risk 1.05, 95% CI 0.78-1.4, P = 0.763). The same result was observed on day 40. Bacteriuria occurred more often in older women with increased length of catheterisation. CONCLUSION: Immediate postoperative prophylaxis with PAC does not reduce the risk of postoperative bacteriuria in patients receiving short-term transurethral catheterisation after pelvic surgery. TWEETABLE ABSTRACT: PAC prophylaxis does not reduce the risk of postoperative bacteriuria in patients undergoing pelvic surgery.