OBJECTIVE: The purpose of this study was to compare the efficacy of 2 different doses of tinidazole with metronidazole for the treatment of bacterial vaginosis and to compare the side effects of the drugs. STUDY DESIGN: Women were assigned randomly to receive metronidazole 500 mg twice daily, tinidazole 500 mg twice daily, or tinidazole 1 g twice, all for 7 days. Follow-up visits were conducted at days 14 and 28. RESULTS: Five hundred ninety-three women were enrolled. There were no significant differences between the treatment arms. Overall cure rates were 76.8% at 14 days and 64.5% at 1 month. Women who admitted to engaging in sexual intercourse during the study were significantly more likely to have bacterial vaginosis at the follow-up visit. There were no significant differences in adverse events across treatment arms. CONCLUSION: There were no differences in cure rates between metronidazole and either of the tinidazole dosing regimens that were studied. In addition, there were no important differences in the side-effect profiles of metronidazole and tinidazole.