In the United States, New York City has had the greatest number of subjects at risk of AIDS for the longest period of time. This population therefore serves as an indicator of changes in cancer risk which may emerge among persons at risk from AIDS. Using a proportional incidence method, we surveyed cancers occurring among single (a surrogate for homosexual) young men and married young men in Manhattan, the rest of New York City, and the remainder of New York State. The baseline period was established earlier to be 1973-76, during which time no cases of Kaposi's sarcoma were ob- served among single men in Manhattan. By 1985, the frequency of Kaposi's sarcoma in this group was increased 1,850fold (compared with expected cases derived from other registries). In the same group, the increase of non-Hodgkin's lymphoma was 6.2-fold (p for trend <O.OOOl), with excesses of Burkitt's lymphoma and immunoblastic lymphoma being most noticeable. Diagnoses of Hodgkin's disease increased markedly in 1985 but not earlier. Since this pattern did not follow that of the AIDS epidemic in this area, we suggest that Hodgkin's disease is not an AIDS-associated tumor. Hepatoma was diagnosed more frequently in single young men during the 1980s but similar increases also were observed in married men and thus may be unrelated to AIDS. Thus, only Kaposi's sarcoma and non-Hodgkin's lymphoma appear to be AIDS-associated tumors, at least so far. With better treatment and longer survival, it remains possible that other tumors will emerge as part of the AIDS epidemic.