A cross-sectional study was conducted among pregnant women from three hospitals in Karachi in order to estimate the prevalence of bacterial vaginosis (BV). Objective.to examine factors associated with BV diagnosis; and to assess the performance of the Amsel criteria (vaginal pH >4.5. Study Design - presence of clue cells; and whiff test) against the Nugent score (score 7.10 by Gram stain). Results - Amsel criteria indicated 7.8% [95% CI = 188.8.131.52] of participants were positive for BV while Nugent score indicated BV in 16.9% [95% CI = 184.108.40.206] of women. The sensitivity and specificity of the Amsel compared with Nugent score were 68% and 94%, respectively. Conclusion - When individual components of the two methods were compared, sensitivity of the Amsel criteria was much lower than using the aggregate criteria. Policymakers should consider the implementation of the Nugent score as a more sensitive and ultimately cheaper diagnostic method for BV among pregnant women in Pakistan. © 2008 MSP International, Inc.