Many donors and countries are striving to respond to the HIV/AIDS epidemic by implementing prevention programmes. However, the resources available for providing these activities relative to needs are limited. Hence, decision-makers must choose among various types of interventions. Cost information, both measures of cost and cost-effectiveness, serves as a critical input into the processes of setting priorities and allocating resources efficiently. This paper reviews the cost and cost-effectiveness evidence base of HIV/AIDS prevention programmes in low- and middle-income countries (LMICs). None of the studies found have complete cost data for a full range of HIV/AIDS prevention programmes in any one country. However, the range of studies highlight the relative emphasis of different types of HIV/AIDS prevention strategies by region, reflecting the various modes of transmission and hence, to a certain extent, the stage of the epidemic. The costing methods applied and results obtained in this review give rise to questions of reliability, validity and transparency. First, not all of the studies report the methods used to calculate the costs, and/or do not provide all the necessary data inputs such that recalculation of the results is possible. Secondly, methods that are documented vary widely, rendering different studies, even within the same country and programme setting, largely incomparable. Finally, even with consistent and replicable measurement, the results as presented are generally not comparable because of the lack of a common outcome measure. Therefore, the extent to which the available cost and cost-effectiveness evidence base on HIV/AIDS prevention strategies can provide guidance to decision-makers is limited, and there is an urgent need for the generation of this knowledge for planning and decision-making.