The random amplified polymorphic DNA technique was used to delineate the genetic relatedness of Trichomonas vaginalis isolates among 3 pairs of mutually infected women who have sex with women in sexual partnerships. One of the 3 pairs of women shared a T. vaginalis isolate with the same random amplified polymorphic DNA banding patterns. Shared use of washcloths to cleanse the vaginal area after receptive oral sex was the most likely method of T. vaginalis transmission among this pair of women.