We investigated the relationship of human papillomavirus (by cervicovaginal lavage and Southern blot), human immunodeficiency virus, and squamous intraepithelial lesions in 96 high-risk women in the Bronx, New York. Antibodies for human immunodeficiency virus were detected in 51 (53%) women. Of the 33 women with symptomatic human immunodeficiency virus infection, 23 (70%) had human papillomavirus infection compared with 4 of 18 (22%) asymptomatic women who were human immunodeficiency virus seropositive and 10 of 45 (22%) uninfected women (p less than 0.0001). The rate of squamous intraepithelial lesions was 52% (14 of 27) for women with both viruses detected, 18% (6 of 34) for women with either virus detected, and 9% (3 of 35) for uninfected women. Among symptomatic human immunodeficiency virus-infected women, a strong association between human papillomavirus infection and squamous intraepithelial lesions was demonstrated (odds ratio, 12; 95% confidence interval, 1.3 to 108). Risk was highest for younger women from ethnic or racial minority groups. Advanced human immunodeficiency virus-related disease, with its associated immunosuppression, seems to exacerbate human papillomavirus-mediated cervical cytologic abnormalities. Public health measures are needed to provide Papanicolaou smear screening and appropriate clinical follow-up and treatment for women at high risk for human immunodeficiency virus infection.