OBJECTIVES: To determine whether cranberry capsules prevent urinary tract infection (UTI) in long-term care facility (LTCF) residents. DESIGN: Double-blind randomized placebo-controlled multicenter trial. SETTING: Long-term care facilities (LTCFs). PARTICIPANTS: LTCF residents (N=928; 703 women, median age 84). MEASUREMENTS: Cranberry and placebo capsules were taken twice daily for 12 months. Participants were stratified according to UTI risk (risk factors included long-term catheterization, diabetes mellitus, >=1 UTI in preceding year). Main outcomes were incidence of UTI according to a clinical definition and a strict definition. RESULTS: In participants with high UTI risk at baseline (n=516), the incidence of clinically defined UTI was lower with cranberry capsules than with placebo (62.8 vs 84.8 per 100 person-years at risk, P=.04); the treatment effect was 0.74 (95% confidence interval (CI)=0.57-0.97). For the strict definition, the treatment effect was 1.02 (95% CI=0.68-1.55). No difference in UTI incidence between cranberry and placebo was found in participants with low UTI risk (n=412). CONCLUSION: In LTCF residents with high UTI risk at baseline, taking cranberry capsules twice daily reduces the incidence of clinically defined UTI, although it does not reduce the incidence of strictly defined UTI. No difference in incidence of UTI was found in residents with low UTI risk.