Bacterial vaginosis is a common, non-inflammatory infection of the vagina. It is characterised by the presence of a thin, homogenous, greyish-white discharge. The differential diagnosis includes infection with Trichomonas vaginalis and Candida albicans. A diagnosis of bacterial vaginosis may be made by the detection of three of the following: characteristic discharge, pH of 5 or greater, clue cells and a positive KOH amine test. Culture of vaginal discharge is not necessary to effect a diagnosis. Bacterial vaginosis responds readily to treatment with metronidazole at a dosage of 400 mg twice daily for seven days, although a proportion of patients suffer a recurrence of symptoms. Treatment of sexual partners may be necessary in such cases. Bacterial vaginosis results from the synergistic interaction of Gardnerella vaginalis and obligate anaerobes, including Bacteroides and Mobiluncus species. The pathogenesis, laboratory diagnosis, treatment, and the mechanisms by which these organisms produce the symptoms of bacterial vaginosis are discussed.