In this review we assess the effectiveness of cranberry and blueberry products in preventing symptomatic urinary tract infections (UTIs). Selection criteria were randomised or quasi-randomised controlled trials of cranberry or blueberry juice/products for the prevention of symptomatic UTIs. A comprehensive search was undertaken in November 2006 whereupon two reviewers independently assessed and extracted data. Quality was assessed using Cochrane criteria. Relative risks (RR) were calculated where appropriate; otherwise a narrative synthesis was undertaken. No relevant trials of blueberry products were identified. Nine trials of cranberry products met the inclusion criteria. In four good quality randomised controlled trials (RCTs), cranberry products significantly reduced the incidence of symptomatic UTIs in 12 months (overall RR 0.65, 95% CI: 0.46-0.90) compared with placebo/control. Five trials were not included in the meta-analyses due to the lack of appropriate data. However, only one reported a significant result. Side effects were common, and losses to followup/withdrawals in several of the trials were high (> 40%). There is some evidence from four good quality RCTs that cranberry juice may decrease the number of symptomatic UTIs over a 12-month period, particularly in women with recurrent UTIs. It is uncertain whether it is effective in other susceptible groups.