Using a mathematical model, the extent of heterosexual HIV-infection in the years 1987-2000 is assessed on the basis of population-based data on sexual behaviour and data from the surveillance system for HIV-infections. The most probable prognosis give about 200 new cases of heterosexual HIV-infection per year at the end of the period, with a prevalence of HIV-infection of about 1,000 persons in the year 2000. According to the prognosis about 50 new cases of heterosexually acquired AIDS will occur per year in the late 1990s. The discrepancy between a high prognosis and a low prognosis is several hundred cases of HIV-infection per year. More precise prognoses will depend on routine collection of population-based data on risk behaviour and spread of infection.