Little is known about the epidemiology of anal human papillomavirus (HPV) infection in women. We studied 251 human immunodeficiency virus (HIV)—positive and 68 HIV-negative women for the presence of anal HPV by use of polymerase chain reaction (PCR) and hybrid capture. Medical and behavioral risk factors were evaluated; 76% of HIV-positive and 42% of HIV-negative women were found to have anal HPV DNA via analysis by PCR (relative risk [RR], 1.8; 95% confidence interval [CI], 1.3–2.5). Among 200 women for whom there were concurrent anal and cervical HPV data, anal HPV was more common than cervical HPV in both HIV-positive (79% vs. 53%) and HIV-negative women (43% vs. 24%). By multivariate analysis of HIV-positive women, CD4+ cell counts ⩽200 cells/mm3, compared with counts >500 cells/mm3 (RR, 1.4; 95% CI, 1.1–1.5), and cervical HPV infection (RR, 1.3; 95% CI, 1.1–1.4) were associated with anal HPV infection. Women >45 years old had reduced risk, compared with women <36 years old (RR, 0.80; 95% CI, 0.50–0.99), as did African American women (RR, 0.86; 95% CI, 0.72–1.0), compared with white women. Anal HPV infection is underrecognized in HIV-positive and high-risk HIV-negative women.