Objective: The purpose of this study was to determine the impact of persistent bacterial vaginosis (BV) on the occurrence of spontaneous preterm birth (SPB) in women who test positive for fetal fibronectin. Study Design: This is a secondary analysis of a subset of pregnant women who tested positive for BV and fetal fibronectin between 160/7 and 256/7 weeks of gestation and who participated in randomized placebo controlled trials of antibiotic therapy. Nugent's criteria were used for the diagnosis of BV. Patients were reassessed for the presence of BV after treatment. The rate of SPB at <34 weeks of gestation was analyzed on the basis of treatment mode and BV status at the follow-up visit. Results: The primary studies included a total of 3285 women. A subset of 215 women met the criteria for this analysis. Seventy-seven of 100 patients (77%) in the antibiotics group vs 33 of the 115 patients (28.7%) in the placebo group became BV negative (P < .0001). The rate of SPB at <34 weeks of gestation was lower for BV resolution compared with persistent BV (0 vs 5.7%, respectively; P = .01). Conclusion: In women who tested positive for fetal fibronectin and BV, resolution of BV is associated with less SPB before 34 weeks of gestation. © 2007 Mosby, Inc. All rights reserved.