The relative contributions of needle use practices and sexual behaviors to human immunodeficiency virus (HIV) antibody seropositivity among 394 women incarcerated in Quebec were determined by risk factor assessment and serology with a nonnominal methodology. HIV positivity was found in 6.9% (95% confidence interval [CI] = 4.6, 9.9) of all participants and in 13% (95% CI = 8.6, 18.6) of women with a history of injection drug use. HIV seropositivity among women with a history of injection drug use was predicted by sexual or needle contact with a seropositive person, self-reported genital herpes, and having had a regular sexual partner who injected drugs, but it was not predicted by prostitution. Nonnominal testing is an ethical alternative to mandatory and anonymous unlinked testing among correctional populations.