Background: Human papillomavirus (HPV) infection of the cervix and related abnormal cervical cytology in HIV-infected women has been well described. Little is known about anal HPV infection in HIV-infected women. Methods: The SUN Study is a prospective cohort study of 700 HIV-infected patients including 167 women. At baseline, patients completed a behavioral questionnaire and provided, among other samples, cervical and anal swabs for HPV detection and genotyping and for cytologic examination. Here, we present the available baseline data on the 167 women in the SUN study. Results: Baseline results were available for 120 women (median age: 38 years, 57% non-Hispanic black, median CD4 cell count 444.5 cells/mm), of whom, 77% were taking antiretroviral therapy. The prevalences in the anus and cervix of any HPV were 90% and 83%, respectively (P = 0.039), and of high-risk (HR) types 85% and 70%, respectively, (P = 0.001). There was no significant difference in the prevalences of abnormal cytology between the anus and cervix: 38% and 33%, respectively (P = 0.217). Although the presence of abnormal cervical cytology was associated with the presence of abnormal anal cytology (relative risk: 1.7, P = 0.024), its sensitivity (52.5%) and positive predictive value positive (45.6%) for identifying women with abnormal anal cytology were poor. A history of anal sex was not associated with anal HPV infection or abnormal anal cytology. Conclusions: In this cohort of HIV-infected women, anal HPV infection was more prevalent and diverse than cervical HPV infection. Anal cytologic abnormalities were as prevalent as cervical cytologic abnormalities, and although abnormal cervical cytology was predictive of abnormal anal cytology, results were not highly concordant. These data support the need for studies of anal cytologic screening of HIV-infected women. Copyright © 2011 American Sexually Transmitted Diseases Association All rights reserved.