The AIDS epidemics is a serious threat to world health. Transmission of infection follows well defined routes: sexual contact with infected people, transfusion of blood or other contaminated products and the transplacental infection. The bulk of cases is due homo or heterosexual contact. Measures to decrease the risk of transmission associated to blood transfusion are already operative in Chile. Campaigns for public education are starting and should be increased. Risky conducts can be decreased by these measures which are the responsibility of society at large.