Background. Bacterial vaginosis (BV) is the most common cause of vaginitis worldwide. Currently recommended treatments have poor efficacy and are associated with high rates of BV recurrence. We examined whether a longer duration of treatment with metronidazole or combination therapy with metronidazole and azithromycin would enhance the cure rates for BV. In addition, we examined factors other than drug therapy associated with cure. Methods. Women with symptomatic BV (defined by a modified Amsel criteria) were enrolled in a 4-arm study that compared metronidazole for 7 days versus 14 days, plus or minus azithromycin on days 1 and 3. Data regarding interim behaviors were also obtained, as were vaginal specimens for Gram staining. Results. At the first follow-up visit (7 days after the completion of therapy), there was a significant difference in cure rates among patients who received 7 days of metronidazole therapy, compared with those who received 14 days of therapy, combined across azithromycin therapy (P = .0003). There was no effect associated with azithromycin therapy. There were no differences in cure rates between any of the treatment groups at 21 days after completion of therapy. Abstinence or protected sex, refraining from douching, and a lower baseline Nugent score for the vaginal Gram stain were all significantly associated with cure. Conclusions. Cure rates for BV were significantly improved by 14 days of metronidazole treatment (compared with 7 days of treatment), but the effects were not sustained, suggesting that relapse or reinfection occurred. Combination therapy with the addition of azithromycin had no benefit. Lower baseline Nugent scores-presumably reflecting less complex vaginal flora-were significantly associated with cure, as was refraining from unprotected sex and from douching. © 2006 by the Infectious Diseases Society of America. All rights reserved.