Cohort study of incident bacterial vaginosis (BV) in Australian students. BV only occurred in vaginally sexually active women (BV incidence = 2.2 [95% confidence interval, 0.8-4.9]/100 woman-years), and no incident BV occurred in women who did not engage in vaginal sex during the cohort period (0 [95% confidence interval, 0-3.2]/100 woman-years), P = 0.10. In university students, incident BV was uncommon and absent in sexually abstinent women.