Routes of transmission of HIV which play an important role in the population are known. Sexual transmission, infection through needle sharing by i.v. drug addicts, accidental blood contacts and transmission from the infected pregnant mother to her child are seen. The number of new infections depends on the number of already infected individuals, the rapidity of spread and the spread potential. The infection can be rapidly spread among drug addicts, several drug users may be infected at the same time through needle sharing. In the general population the spread potential through sexual transmission is high. The AIDS prevention campaign in Switzerland aims at preventing new infections and at building up solidarity. With the STOP-AIDS campaign a broad effect in the population could be reached. The most important goals in the near future are to have an effect in depth in some target groups and to promote individual counselling.