What is known about the occurrence of sexually transmitted infections (STI) in women who have sex with women (WSW), and should it matter? Demographically, this is not a trivial issue: estimates of lifetime same sex behaviour among women range from 8% to 20%, and between 1.4% and 4.3% of all women may be WSW on the basis either of behaviour or self defined identity.^1–3 WSW have traditionally been viewed as “low risk” for STI, including HIV, and data from several small studies seem to support this belief.^4–9 However, as is often the case when one attempts to categorise any group by a descriptive “measurement” as complex as sexual behaviour, the real situation is of course more complicated.

As several studies have reported, the sexual practices of WSW present a reasonable means for vagina to vagina transmission of infected cervicovaginal secretions,^10–12 a concept most directly supported by documentation of trichomoniasis being sexually transmitted between women.¹³ There is strong evidence that transmission of human papillomavirus (HPV) between female sex partners occurs, as HPV and associated squamous intraepithelial lesions (SIL) have been detected in WSW who reported no previous sex with men.^10,14,15 Bacterial vaginosis (BV), a condition associated with pelvic inflammatory disease and adverse outcomes of pregnancy,¹⁶ occurs in 24% to 51% of WSW,^5,9,12,17,18 and sexual transmission of some responsible factor has been debated.^12,17 Although uncommon, transmission of HIV and hepatitis B between female sex partners has been reported.^19–23 Many WSW are also at risk for STI acquisition from male partners. Even when surveyed outside STI clinic settings, most WSW report having had sex with men, and many (20–30%) continue to have sex with men as well as women. …