To clarify further the epidemiology of AIDS-related Kaposi's sarcoma (KS) in San Francisco, we reviewed AIDS cases reported to the San Francisco Department of Public Health through August 31, 1990. Of the 7,119 patients reported, 2,346 (33%) had been diagnosed as having KS: 1,716 (73%) as their presenting clinical manifestation of AIDS and 648 (27%) as a later manifestation. Of these 2,364 KS patients, 2,075 (88%) were homosexual or bisexual men without histories of intravenous drug use, and 273 (12%) were homosexual or bisexual intravenous drug users. From 1981 to August 1989, the proportion of AIDS patients presenting with KS declined from 55 to 19% (p less than 0.001). However, the number of patients being diagnosed with KS has increased along with the overall number of AIDS patients, but this increase was less than the increase in number of patients with other opportunistic infections and malignancies. KS patients were less likely than patients without KS to be reported through an active surveillance system and less likely to be found through retrospective reviews of medical records, death certificates, and obituaries. We conclude that the proportion of AIDS patients with KS is continuing to decline in San Francisco and that this decline is not an artifact of the AIDS surveillance system.