A computer simulation of the morbidity and mortality rates of the "Acquired Immunodeficiency Syndrome" in the Federal Republic of Germany was performed. Since sexual intercourse is the main mode of transmission, the population was divided into six groups with different sexual behaviour. In several variations of the program it is demonstrated that during the next 15 years up to 41,000 AIDS patients can be expected. The importance of female prostitutes and male bisexuals as "vectors" who may transmit the infection into exclusively heterosexual groups is shown. Using this program, the effect of prophylaxis against infection as well as of changes of sexual behaviour within the population at large can also be examined.