Sexual transmission of bacterial vaginosis (BV), a common syndrome in sexually active women, has not been previously established. Because no male counterpart for BV has been found, a population of lesbians is an ideal one in which to test the hypothesis that BV is sexually transmitted. We studied 103 homosexual women (lesbians) who sought gynecologic care at a community clinic and in a private gynecology practice in New York City. Participants were asked to refer their sexual partners for evaluation. In this cross-sectional prevalence study, all participants were evaluated for the presence of BV, and pairs of monogamous sexual partners were analyzed for concordance of their vaginal secretions. Twenty-nine (28.7%) of the 101 participants from whom satisfactory vaginal wash samples were available had BV. There were 21 pairs of monogamous partners. Of 11 index women who had BV, eight (72.7%) had partners who also had BV. Of 10 index women who did not have BV, only one (10%) had a partner with BV. The likelihood of a partner's having BV was 19.7 times greater if the index case had BV (P < .008; 95% CI, 2.1-588.0). We conclude that with respect to BV, lesbians in monogamous relationships usually have concordant vaginal secretions. This concordance probably reflects the sexual transmission of BV between lesbians.