A retrospective survey of women treated in prison for trichomonal vaginitis with metronidazole showed that 488 of 496 (98·3%) were cured after one course of drugs. Five of the eight treatment failures were successfully treated by further courses of metronidazole. A regimen of 400 mg metronidazole twice daily for seven days is simple and effective when taken in prescribed dosage. Metronidazole is still the drug of choice for trichomonal vaginitis. No toxic reactions were observed and there was no evidence that the drug has lost efficacy in the last ten years.