Marijuana use was recently reported to have a positive cross-sectional association with human papillomavirus (HPV)-related head and neck cancer. Laboratory data suggest that marijuana could have an immunomodulatory effect. Little is known, however, regarding the effects of marijuana use on cervical HPV or neoplasia. Therefore, we studied the natural history (i.e., prevalence, incident detection, clearance/persistence) of cervical HPVand cervical neoplasia (i.e., squamous intraepithelial lesions; SIL) in a large prospective cohort of 2,584 HIV-seropositive and 915 HIV-seronegative women. Marijuana use was classified as ever/ never, current/not current, and by frequency and duration of use. No positive associations were observed between use of marijuana, and either cervical HPV infection or SIL. The findings were similar among HIVseropositive and HIV-seronegative women, and in tobacco smokers and nonsmokers. These data suggest that marijuana use does not increase the burden of cervical HPV infection or SIL.