To determine the diagnostic accuracy of Nugent's score and each Amsel's criterion in the diagnosis of bacteria vaginosis (BV), considering Amsel's criteria as the gold standard. Cross-sectional, descriptive study (diagnostic test) Setting: Family planning clinic, Siriraj Hospital, Mahidol University. A total of 217 women who attended the Family Planning Clinic at Siriraj Hospital between August and December 2003. Pelvic examination was performed on each participant. Samples of vaginal discharge was tested for BV infection using both Amsel's criteria and Nugent's score. Interpretation was made blinded without knowledge of each test result. Using Amsel's criteria as a gold standard, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of Nugent's score and each of Amsel's criteria were estimated. Considering Amsel's criteria as the gold standard, Nugent's score showed a sensitivity of 65.6% (95%CI 46.8%, 80.8%), specificity of 97.3% (95%CI 93.5%, 99.0%), positive predictive value (PPV) of 80.8% (95%CI 60.0%, 92.7%), negative predictive value (NPV) of 94.2% (95%CI 89.7%, 96.9%) and accuracy of 92.6% (95%CI 88.1%, 95.6%). Both vaginal pH and whiff test demonstrated 100% sensitivity. However, vaginal pH showed lower specificity than the whiff test (58.9% and 97.3% respectively). Nugent's score might not be suitable to use as a screening test for diagnosis of BV due to its low sensitivity. The whiff test is the best clinical criteria of Amsel's criterion in the diagnosis of BV due to its high sensitivity and specitivity.