Summary Studying factors influencing the length of the incubation period of HIV/AIDS is important to our understanding of the natural history of the disease and for the decision when to start with anti-retroviral therapy. In a multicentre study among HIV-positive homosexual men with a known date of seroconversion, we found that the median survival time after HIV infection was 12.1 years. Age is an important determinant of the survival: the older the shorter the incubation period and survival. Gender does not seem to play a role, but women appear to have higher CD4 counts than men at seroconversion, AIDS and death. HIV-positive drug users often die before they ‘reach’ AIDS often from HIV-related causes e.g. bacterial infections. In a multicentre study we found that such pre-AIDS mortality is now also found among homosexual men and haemophiliacs but at a much lower level. Most studies show that HIV subtype does not influence the incubation period. On the other hand genetic factors do play an important role.