Objective: To further examine the hypothesis that Kaposi's sarcoma (KS) among people with AIDS is caused by a sexually transmissible infectious agent. Design: Analysis of Australian AIDS surveillance data for the period 1982–1991 by sex, age, exposure category, country of birth, year and place of diagnosis. Main outcome measures: Percentage of people with AIDS who had KS. Results: In Australia, by November 1991, 17.2% (527 out of 3067) of individuals with AIDS aged ≥ 13 years had presented with KS as their AIDS-defining illness: men, 17.6% (524 out of 2977); women, 3.4% (three out of 87) (P2 for a linear trend, PP7:1667–1671