OBJECTIVE: This study was undertaken to determine whether asymptomatic bacterial vaginosis (BV) is associated with an increased risk of endometrial microbial colonization or plasma cell endometritis in nonpregnant women. STUDY DESIGN: In this observational cohort study conducted between August 1995 and August 2001, microbial cultures (n = 769) and histopathology (n = 482) were performed on endometrial specimens obtained from women with a recent preterm or term delivery (83 +/- 16 days). Endometritis was defined as the presence of plasma cells. BV was defined using Amsel and Nugent criteria. RESULTS: The study population was 71% black, 29% white, 69% single, and 31% had 12 years or more of education. Endometrial cultures were positive for at least 1 microorganism in 83% (n = 637/769) of the women and plasma cell endometritis was present in 39% (n = 190/482). BV was present in 26% (n = 191/722) by Amsel and 38% (n = 289/769) by Nugent criteria. Women with Nugent-BV (RR [relative risk] = 1.12, 95% CI 1.05-1.19) but not Amsel-BV (RR = 1.06, 95% CI 1.00-1.13) were significantly more likely to have a positive endometrial culture. A consistent and significant association was observed between BV (by Amsel or Nugent criteria) and an increased frequency of endometrial colonization with BV-associated microorganisms grouped and defined in various ways (RR ranged from 1.96-4.22). No association between BV and plasma cell endometritis was observed. CONCLUSION: Asymptomatic BV is associated with a modest increased likelihood of endometrial microbial colonization and colonization by BV-associated bacteria but is not associated with plasma cell endometritis in nonpregnant women.