Statistical methods to estimate HIV infection rates by working backwards from AIDS incidence (known as back-calculation) were improved. The refined methods fully incorporate uncertainty about the natural history, account for competing mortality, and provide smooth reconstructions of HIV incidence. In a validation study, back-calculation provided estimates of HIV incidence among U.S. hemophiliacs that were consistent with estimates derived from a large cohort study of hemophiliacs. A detailed assessment was made of HIV incidence trends among adolescents and young adults in the United States using back-calculation from AIDS data. A manuscript describing the results has been submitted for publication. The study showed that among young persons 20-25 years of age, HIV incidence in homosexual men and injection drug users was slowing by 1993. However, this favorable trend was offset by increasing heterosexual transmission, especially to minority teenagers. Overall, HIV prevalence in 20-25 year olds was estimated to have declined by only 14% between 1988 and 1993. Among HIV-infected persons with hemophilia, the nature of the AIDS-defining condition was found to be as important as age at seroconversion and CD4+ level in predicting post-AIDS survival. Subjects with HIV-associated neurologic disease had the worst prognosis. The survival experience of HIV-infected children with cancer was characterized using a case series from the Children's Cancer Group and the National Cancer Institute.