To develop a model for predicting acquired immunodeficiency syndrome (AIDS) morbidity in San Francisco, Calif, through June 1993, we combined annual human immunodeficiency virus seroconversion rates for homosexual and bisexual men and for heterosexual intravenous drug users with estimates of the cumulative proportion of the population with AIDS by duration of human immunodeficiency virus infection and with estimates of the size of the at-risk populations. We projected AIDS mortality by applying Kaplan-Meier estimates of survival time following diagnosis to the projected number of cases. The median incubation period for AIDS among homosexual and bisexual men infected with the human immunodeficiency virus was estimated to be 11.0 years (mean, 11.8 years; 95% confidence interval, 10.6 to 13.0 years). The model projects 12,349 to 17,022 cumulative cases of AIDS in San Francisco through June 1993, with 9,966 to 12,767 cumulative deaths.