To evaluate the association between preterm labor and bacterial vaginosis. Materials & methods:A total of 100 pregnant women who had no known medical risk factors for preterm delivery were enrolled. At 23 to 26 weeks' gestation, bacterial vaginosis was determined to be present or absent on the basis of the vaginal pH and the results of Gram's staining. The principal outcome variable was the delivery at less than 37 weeks' gestation of an infant with a birth weight below 2500 g. All the results were recorded in Microsoft excel sheet and were subjected to statistical analysis using SPSS software. Results:Bacterial vaginosis was detected in 23 percent of the 100 women. The women with bacterial vaginosis were more likely to be unmarried and low socio-economic status. In a multivariate analysis, the presence of bacterial vaginosis was related to preterm delivery of a low-birth-weight infant. Out of 53 subjects with presence of preterm labour, bacterial vaginosis was seen in 7.55 percent of the patients. Conclusion:Bacterial vaginosis was associated with the preterm delivery of low-birth-weight infants independently of other recognized risk factors.