<<<!!!<<< stated 26-02-2020: Amsterdam Cohort Studies on HIV infection and AIDS is no longer available online >>>!!!>>> The Amsterdam cohort study (ACS) on human immunodeficiency virus (HIV) infection and AIDS among homosexual men started in 1984 and was expanded to include drug users in 1985. Thus far, about 2100 homosexual men and 1630 (injecting) drug users have been included of whom approximately 700 homosexual men and 550 drug users are still in active follow-up. Every 3-6 months participants complete a standardized questionnaire to obtain medical, epidemiological and social scientific information and undergo a medical examination. In addition, they have blood drawn for virological and immunological tests and storage.