The epidemiology of hepatitis B in female prostitutes was studied in a cross-sectional survey of 467 prostitutes and 510 control prenatal clinic patients from Lima and Iquitos, Peru. Prostitutes reported a mean of 8.8 ± 6.7 years of active prostitution and a mean of 205 ± 137 sexual contacts in the month prior to the study. Hepatitis B surface antigen (HBsAg) was found in comparable percentages of prostitutes (1.7%) and controls (0.8%; P =.305). In contrast, seropositivity for both antigen and antibody markers (HBsAg, anti-HBs, or anti-hepatitis Bcore) was found in a significantly higher percentage of prostitutes than controls (67.0% vs. 10.0%; P <.0001). By multivariate analysis, both prostitution (odds ratio [OR] 14.6) and the number of years of exposure as a prostitute (OR 3.2 for 10 years of exposure at age 35 years) were significantly associated with seropositivity for hepatitis B markers when adjusted for age. In this study, the prevalence of HBsAg was not substantially increased in highly active female prostitutes compared with the general population, even though hepatitis B transmission was greatly increased. These data suggest that in adult women with a high level of hepatitis B infection, hepatitis B antigenemia may not persist as frequently as previously indicated in studies of other populations. © 1990, by The University of Chicago.