ObjectiveTo examine the role of initial AIDS-defining illness in survival following AIDS and survival trends over time.DesignStates and Territory Health Departments notified new diagnoses of AIDS to the National AIDS Registry. Information on vital status and date of last medical contact was sought annually.MethodsSurvival was calculated for all adult and adolescent AIDS cases (n = 3204) in Australia diagnosed until 1 November 1991 and reported to the National AIDS Registry by 31 March 1994. The Cox regression method was used to identify independent predictors for survival.ResultsAge < 50 years, a CD4+ cell count >100 × 106/l and an initial diagnosis of Kaposi's sarcoma were independently associated with longer survival (P<0.05). Acquisition of HIV through blood transfusion and the AIDS-defining illness non-Hodgkin's lymphoma were significantly associated with shorter survival. Survival improved substantially from 1986 to 1987, but did not improve further thereafter. A further study of initial AIDS-defining illnesses in a subgroup of individuals, i.e., men aged <50 years at diagnosis who acquired HIV infection through homosexual or bisexual contact and diagnosed after 1987, showed that Kaposi's sarcoma,Pneumocystis cariniipneumonia, oesophageal candidiasis and herpes simplex virus as initial AIDS-defining illnesses had a relatively better prognosis than other single illnesses. Furthermore, patients with multiple illnesses did not have a worse prognosis than patients with a single illness, provided all illnesses were those with a better prognosis.ConclusionsInitial AIDS-defining illness, as well as age at diagnosis, year of diagnosis, HIV exposure and CD4+ cell count at diagnosis, plays an important role in survival following AIDS in Australia.