Tracking the natural history of HIV/AIDS in the hemophilia community is useful for planning future health care needs and for adjusting estimates of the prevalence of hemophilia as the impact of HIV/AIDS wanes over time. The present study was designed to determine the annual prevalence of HIV infection from 1988 through 1997 in a population of males with hemophilia A or B. Data were obtained from the Oklahoma Hemophilia Surveillance System and were limited to individuals who were seen at the Oklahoma Hemophilia Treatment Center. In 1988, the prevalence rate of HIV infection was 34 percent. Rates have declined in each subsequent year through 1997. The highest rates of HIV infection were observed in persons with severe hemophilia and hemophilia A. The overall prevalence rates of HIV infection in this treatment center population are lower than those reported in other populations. No new cases of HIV infection were observed in persons with hemophilia born after 1985.