A Peruvian female prostitute population was evaluated over a 3-year period to determine the incidence and risk factors of retroviral and viral hepatitis transmission. At three survey periods, a questionnaire was administered and serum samples were obtained. A total of 966 subjects were studied, with 34% followed for 38 months, 22% followed for 18 months, and 44% evaluated just once. On initial evaluation, 3 (0.3%) had HIV-1 antibody, 170 (17.6%) had HTLV-I antibody, 578 (59.8%) had anti-HBc, and 7 (0.7%) had antibody to hepatitis C virus. The mean annual incidence of HTLV-I and hepatitis B infection was 1.6% and 4.7%, respectively. Univariate and logistic regression analysis of prevalence data indicated an association between sexual activity and HTLV-I and hepatitis B infection, but no independent risk factors were identified in cohort analysis. Parenteral risk factors were not associated with transmission, except for a small percentage of subjects who may have acquired hepatitis B infection from blood transfusions. These findings suggest that there is a high incidence of HTLV-I and hepatitis B infection from heterosexual contact in this female prostitute population.