This study briefly reviews Gardnerella vaginalis as a primary vaginal pathogen and assesses the efficacy and safety of therapy with a single, 2-g oral dose of metronidazole. Over a period of 20 months, 882 symptomatic adolescent girls had positive cultures for G. vaginalis. All were post-menarcheal. No other vaginal pathogen was isolated in 609. The total group had a second culture 5-7 days after treatment. Cultures taken after treatment were negative in 95% of those treated with a single 2-g dose of metronidazole. Symptoms abated with therapy and culture negativity. Side effects were limited to infrequent, minor gastric distress. Our results suggest the utility of a simplified, one-dose regimen with high efficacy, insignificant side effects, and a lower cost per patient than the current dosage schedule of 500 mg b.i.d. for 7 days.