The objective of this study was to examine factors, including human immunodeficiency virus (HIV) infection, associated with ectopy among adolescent girls aged 12-20 years who were participating in an ongoing study of HIV infection in adolescents. Samples for detection of bacterial vaginosis, Chlamydia trachomatis, and Neisseria gonorrhoeae and a high-resolution photograph of the cervix for ectopy measurement were collected. Ectopy data for 189 and 92 HIV-positive and -negative adolescents, respectively, were examined. Although univariate analysis found HIV infection and oral contraceptive use to be associated with the amount of ectopy, multivariate logistic regression analysis showed that only number of lifetime sex partners was a significant predictor, with more partners associated with less ectopy (odds ratio, 0.47; 95% confidence interval, 0.22-1.00; P=.05). In summary, adolescent girls with greater numbers of lifetime sex partners were more likely to have mature cervixes (less ectopy). HIV infection was not independently associated with ectopy.