Trichomoniasis has been implicated in the acquisition and transmission of human immunodeficiency virus (HIV) infection. The prevalence, incidence, and persistence or recurrence of trichomoniasis were assessed among HIV-positive women and among HIV-negative women at high risk for HIV infection. A total of 871 HIV-seropositive women and 439 HIV-seronegative women enrolled in the HIV Epidemiology Study (HERS) were seen biannually. The prevalence of trichomoniasis was 9.4%-29.5% among HIV-seropositive women and 8.2%-23.4% among HIV-seronegative women. Prevalence decreased over time, did not vary according to HIV status or CD4 cell count, and was higher among women who reported crack use (P=.02) or cigarette use (P=.02), women who had bacterial vaginosis (P=.02), and those who were black (compared with white women, P<.001). There were no differences, according to HIV status or CD4 cell count, in the adjusted incidence, unadjusted incidence, or persistence or recurrence of trichomoniasis. HIV infection does not make a woman more likely to have prevalent, incident, or persistent or recurrent trichomoniasis.