Objective: The purpose of this study was to assess the association of psychosocial stress with bacterial vaginosis in a longitudinal sample of nonpregnant women. Study design: A 1-year prospective longitudinal design was used. Nonpregnant women (n = 3614) aged 15 to 44 years were recruited at routine health care visits. Assessments were conducted quarterly for 1 year and included a standardized pelvic examination, an assessment of clinical symptoms, and an extensive self-report interview. Results: Psychosocial stress was associated with overall prevalence of (adjusted odds ratio, 1.10; 95% CI, 1.01-1.20) and an increased incidence of (adjusted odds ratio, 1.29; 95% CI, 1.12-1.48) bacterial vaginosis. The association between stress and bacterial vaginosis incidence was not changed appreciably by the control for behavioral and demographic characteristics and was magnified (odds ratio, 2.05; 95% CI, 1.15-3.66) in a case-crossover analysis. Conclusion: Increased psychosocial stress is associated with greater bacterial vaginosis prevalence and incidence independent of other risk factors. © 2006 Mosby, Inc. All rights reserved.