The objective was to study changes in the occurrence of human immunodeficiency virus type 1-related Kaposi's sarcoma and the association with degree of immunodeficiency over time. Danish patients with acquired immunodeficiency syndrome (AIDS) diagnosed between 1979 and 1990 (n = 687) were followed clinically and with consecutive CD4 cell count measurement from time of AIDS-defining illness to date of death or censoring date, whichever came first. The proportion of homo-/bisexual men (n = 520) with Kaposi's sarcoma (n = 100) at AIDS diagnosis declined from 31% before 1985 to 13% in 1990, whereas the proportion of patients who died with Kaposi's sarcoma remained constant over time. Furthermore, the CD4 cell count at time of AIDS for patients diagnosed with Kaposi's sarcoma has declined in recent years. A CD4 cell count < 200 x 106/liter at the time of AIDS diagnosis predicted an increased risk of developing Kaposi's sarcoma after the AIDS diagnosis. Age, antiretroviral therapy, and primary Pneumocystis carinii pneumonia prophylaxis failed to influence the development of Kaposi's sarcoma. Thus, the occurrence of Kaposi's sarcoma remained constant over time but developed later in the course of AIDS and was associated with more severe immunosuppression in recent years.