Little is known about the epidemiology of human herpesvirus 8 (HHV-8) infections among women. A cross-sectional study was conducted of HHV-8 infection among human immunodeficiency virus (HIV)-infected and high-risk HIV-uninfected women. Serological tests with noninduced (latent) and induced (lytic) HHV-8 antigens were used to detect infection among 2483 participants of a multisite cohort. Reactivity to latent antigen was present in 4.1% and to induced antigens in 12.0% of women. Seven of 8 women who reported Kaposi's sarcoma had HHV-8 antibodies. Among HIV-positive women, HHV-8 infection was associated with use of crack, cocaine, or heroin (76% vs. 65%; P<.001), past syphilis (29% vs. 20%; P<.001), an injection drug-using male sex partner (61% vs. 53%; P=.014), black race (P=.010), and enrollment site (P=.015). In multivariate analysis, HIV infection, older age, past syphilis, black race, and enrollment site were independently associated with HHV-8 infection. In this cohort of North American women, HHV-8 infection was associated with HIV infection, drug use, and risky sexual behavior.