Despite considerable advances in understanding the basic biology of the human immuno-deficiency virus, the aetiological agend of AIDS, medical, public health and health education planning continues to be plagued by uncertainties. There remain many questions of an epidemiological nature to be answered. The questions to be addressed include, how many people are HIV positive? What groups are most vulnerable? Where should valuable intervention policies be directed? Mathematical models of the dynamics of HIV transmission and its progression to AIDS can clarify what data must be collected in order to predict future prevalence, make predictions about the likely effect of future intervention policies and provide predictions for several decades ahead. This is a good example of how mathematics can be used to assist in the preservation of human life.