To determine whether recurrences of urinary tract infection can be prevented with cranberry-lingonberry juice or with Lactobacillus GG drink. Open, randomised controlled 12 month follow up trial. Health centres for university students and staff of university hospital. 150 women with urinary tract infection caused by Escherichia coli randomly allocated into three groups. 50 ml of cranberry-lingonberry juice concentrate daily for six months or 100 ml of lactobacillus drink five days a week for one year, or no intervention. First recurrence of symptomatic urinary tract infection, defined as bacterial growth >/=10(5 )colony forming units/ml in a clean voided midstream urine specimen. The cumulative rate of first recurrence of urinary tract infection during the 12 month follow up differed significantly between the groups (P=0.048). At six months, eight (16%) women in the cranberry group, 19 (39%) in the lactobacillus group, and 18 (36%) in the control group had had at least one recurrence. This is a 20% reduction in absolute risk in the cranberry group compared with the control group (95% confidence interval 3% to 36%, P=0.023, number needed to treat=5, 95% confidence interval 3 to 34). Regular drinking of cranberry juice but not lactobacillus seems to reduce the recurrence of urinary tract infection.