A lesbian couple in a monogamous relationship each presented with vaginal discharge demonstrable on culture to contain Trichomonas vaginalis. Their symptoms had failed to respond to standard regimens of metronidazole, and subsequent microbiological sensitivities confirmed resistance of the trichomonads to metronidazole (minimum inhibitory concentrations in aerobic conditions > 8 mcg/ml). In addition, the couple denied use of penetrative sex toys or recent male partners, supporting the concept of transmission through mutual masturbation.