Certain types of the human papillomavirus (HPV) are sexually transmitted and cause genital warts and cervical neoplasia. Little is known about the epidemiology of HPV among women who have sex with women (WSW), but recent research using amplified techniques for HPV DNA strongly suggests that HPV is sexually transmitted between female sex partners. In a pilot study of 149 WSW in Seattle, Washington, prevalence of HPV as detected by DNA amplification assay was 30%, and was 19% among women reporting no prior sex with men. Although most cervical cancer can be prevented with Pap smear screening by detection of squamous epithelial lesions (SIL), some data suggest that the frequency of Pap smear screening is suboptimal in WSW. Reasons for this are unclear, but may include perceptions by patients and providers that WSW are not at risk for many STD and, by extension, cervical cancer. In our study, WSW who reported no prior sex with men had routine Pap smear screening less frequently than the comparative group, and had a prevalence of SIL of 14%. Combined with the work of other investigators, these data strongly suggest that current recommendations for Pap smear screening among WSW should not differ from those for heterosexual women. WSW and their providers should understand that sex between women may confer a risk of HPV transmission; risk of transmission of other STD, including HIV, deserves further study.