ObjectiveTo analyse the influence of age at seroconversion and sexual exposure group on the progression of HIV disease.DesignThis multicentre prospective cohort study involved 443 subjects whose date of HIV infection was known to within ±1 year. Individuals whose sexual behaviour was exclusively heterosexual after HIV infection constituted the heterosexual group (n = 131). AIDS-free survival was compared with that of men (n = 312) infected through homosexual sex and who continued homosexual activity after HIV infection. They constituted the homosexual group.MethodsThe end-point was the onset of an AIDS-defining illness listed in the 1987 revised Centers for Disease Control and Prevention (CDC) criteria. Using the Kaplan-Meier method, AIDS-free survival curves were plotted for three age categories ( < 20, 20–39, >40 years). A Cox model was used to quantify the effect of age and to assess the influence of exposure group on AIDS onset after adjustment for age. Because of the high incidence of Kaposi's sarcoma (KS) among homosexual men, a disease that can be an early AIDS-defining illness, multivariate analysis was performed with and without consideration of the occurrence of KS.ResultsPatients aged ≥40 years at seroconversion progressed more rapidly to AIDS than younger patients (P< 0.006). When age was fitted as a continuous variable and adjusted for exposure group, the relative risk of developing AIDS by any time after seroconversion was 1.34 for a 10-year increase difference [P= 0.03; 95% confidence interval (Cl), 1.03–1.77]. After adjustment for age, the relative risk of developing AIDS (CDC criteria) was 2.42 (P= 0.008; 95% Cl, 1.18–4.97) among the homosexual men (AIDS cases, n = 56). All cases of KS (n = 19) involved the homosexual group. Excluding KS as a first manifestation of AIDS, homosexual or bisexual subjects had a risk of AIDS of 1.92 (P=0.07; 95% Cl, 0.92–4.03) compared with heterosexual subjects.ConclusionsThe risk of AIDS increases with age at seroconversion. The more rapid progression towards AIDS in the homosexual group than in the heterosexual group persisted after adjustment for age. Further studies are required to determine the possible role of repeated exposure to HIV or other pathogens acquired sexually.