The rationale for this paper was that projections of the size of the AIDS epidemic are of major importance for future health care and prevention. Projections were made in this article based on the back-projection method. Data on the incidence of AIDS, since the epidemic had started in Ireland in 1982, were examined, and separate predictions were made for the two largest risk groups in Ireland - homosexual/bisexual and intravenous drug users (IDUs). The predictions showed an overall increase in rates, with the rate of increase for IDUs being higher than that for the homo/bisexual group. The authors expected to see a total of 1,100 IDU AIDS cases by the year 2001, and a total of 720 cases among the homo/bisexual group.