Bacterial vaginosis (BV) is a common cause of vaginitis and increases women's risk of pelvic inflammatory disease, adverse pregnancy outcomes, and risk of STD/HIV acquisition. The etiology of BV is unclear, though it is believed to involve loss of vaginal hydrogen peroxide-producing lactobacilli and acquisition of complex bacterial communities that include many fastidious BV-associated bacteria (BVAB) that have recently been detected using PCR methods. Treatment failure (persistence) is common, and may be facilitated by unprotected sex. Potential contributions to BV and BV persistence include (1) sexual partners as a reservoir for BVAB; (2) specific sexual practices, including male partners' condom use; and (3) the composition of the vaginal microbiota involved in BV. Specific BVAB in the Clostridiales order may predict BV persistence when detected pre-treatment, and have been detected in men whose female partners have BV. BVAB may be associated with unprotected sexual behavior and failure of BV to resolve in women, supporting the hypothesis that BVAB colonization of male genitalia may serve as a reservoir for re-infection of female partners. Moreover, specific sexual practices may favor vaginal colonization with certain BVAB that have been associated with persistence. This review provides background on BV, and discusses the epidemiologic and microbiologic data to support a role for acquisition of BVAB and how this process might differ among subsets of women. © 2011 Elsevier Ltd.