Background: Whether bacterial vaginosis (BV) is sexually transmitted is uncertain. Also it is unknown why BV is approximately twice as prevalent among black as among white women. An association of BV with a characteristic of the male sex partner, such as race, might support sexual transmission as well as account for the observed ethnic disparity in BV. Methods: Three thousand six hundred twenty nonpregnant women 15 to 44 years of age were followed quarterly for 1 year. At each visit, extensive questionnaire data and vaginal swabs for Gram's staining were obtained. The outcome was transition from BV-negative to positive (Nugent's score ≥7) in an interval of 2 consecutive visits. Results: BV occurred in 12.8% of 906 sexually active intervals to white women-24.8% of intervals when the woman reported a black partner and 10.7% when all partners were white. Among white women, there was a 2-fold increased risk for BV incidence with a black, compared with a white partner (risk ratio [RR] 2.3, 95% confidence interval 1.6-3.4; adjusted RR 2.2, 95% confidence interval 1.5-3.4), but differed according to condom use. In the presence of consistent condom use, the adjusted RR was 0.7 (0.3-2.4); it was 2.4 (1.0-6.2) in the presence of inconsistent use; and 2.7 (1.7-4.2) in the absence of condom use. Black women could not be studied, as there were insufficient numbers who reported only white male sex partners. CONCLUSION: The association of BV occurrence with partner's race, and its blunting by condom use, suggests that BV may have a core group component and may be sexually transmitted. Copyright © 2010 American Sexually Transmitted Diseases Association All rights reserved.