Prior to the AIDS epidemic, Kaposi's sarcoma (non-AIDS-KS) in Europe was mainly a disease of elderly Mediterranean men. In 1989 AIDS data from 15 European countries were collected to study proportional trends in AIDS-related Kaposi's sarcoma (AIDS-KS) in order to determine whether specific factors in Southern Europe might be important in the development of KS among AIDS patients. Another AIDS-related cancer, non-Hodgkin's lymphoma (NHL) was included as a malignancy control. Of 22,367 AIDS cases reported, 3,779 (16.9%) were KS and 741 (3.3%) were NHL. A significant, continuous fall in the percentage of AIDS-KS was seen for both homosexual men and other members of exposure groups during the period 1981-89 (p-trend <0.000l). The proportion with AIDS-KS decreased from 40.5% in 1983 to 26.5% in 1988 in homosexual men and from 12.2 to 3.6% in other exposure groups, respectively. No significant change was observed in the proportion of NHL cases among any of the risk groups over time, although a tendency towards a slight increase was noted for homosexual men. Comparing proportional trends of KS and NHL geographically, no significant difference was found overall, by time or by exposure group. In conclusion, a specific decline is observed over time for AIDS-KS. However, if geographically-restricted factors are important in the development of non-AIDS-KS in Europe, the same factors do not appear to affect the risk of AIDS-KS.