OBJECTIVES: This study examined whether hormonal contraceptive use is associated with diagnosis of bacterial vaginosis (BV) over 1 year. STUDY DESIGN: A total of 3077 women of reproductive age were recruited from gynecologic and family planning clinics for a 1-year prospective longitudinal study. Data collected over 5 visits included demographics, health and hygiene behaviors, and gynecological exams. Gram stains were used to quantify vaginal flora. RESULTS: There was a decreased risk of overall BV prevalence among oral contraceptive users (odds ratio, OR 0.76; confidence interval, CI 0.63-0.90) and among those using hormonal injection/implant (OR 0.64; CI 0.53-0.76). An increased risk for BV prevalence (OR 1.38; CI 1.11-1.71) and incidence (OR 1.43; 1.02-2.07) was observed among those subjects who had tubal ligation. Greater remission of BV was found among those using hormonal injection or implant (OR 1.67; CI 1.23-2.27) whereas less remission occurred among those subjects who had tubal ligation (OR 0.56; CI 0.39-0.80). CONCLUSIONS: Hormonal contraceptive use is associated with a decreased risk of BV. © Copyright 2007 American Sexually Transmitted Diseases Association.