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We used data from Europe, North America, and Australia to assess the effect of exposure category on the AIDS incubation period and HIV-1 survival and whether the effect of age at seroconversion varies with exposure category and with time since seroconversion.38 studies of HIV-1-infected individuals whose dates of seroconversion could be reliably estimated were included in the analysis. Individual data on 13 030 HIV-1-infected individuals from 15 countries were collated, checked, and analysed centrally. We calculated estimates of mortality and AIDS incidence rates and estimated the proportions of individuals surviving and developing AIDS at each year after seroconversion from the numbers of observed deaths or cases of AIDS and the corresponding person-years at risk. Analyses were adjusted for age at scroconversion, time since scroconversion, and other factors as appropriate.Mortality and AIDS incidence increased strongly with time since seroconversion and age at seroconversion. Median survival varied from 12.5 years (95% CI 12.1-12.9) for those aged 15-24 years at seroconversion to 7.9 years (7.4-8.5) for those aged 45-54 years at seroconversion, whereas for development of AIDS the corresponding values were 11.0 years (10.7-11.7) and 7.7 years (7.1-8.6). There was no appreciable effect of exposure category on survival. For AIDS incidence, the exposure category effect that we noted was explained by the high incidence of Kaposi's sarcoma in those infected through sex between men. We estimated that among people aged 25-29 years at seroconversion 90% (89-91) and 60% (57-62) survived to 5 years and 10 years, respectively, after seroconversion, whereas 13% (12-15) and 46% (44-49), respectively, developed AIDS (excluding Kaposi's sarcoma).Before widespread use of highly-active antiretroviral therapy (before 1996), time since seroconversion and age at seroconversion were the major determinants of survival and development of AIDS in Europe, North America, and Australia.