The objective of this thesis is to undertake a cost analysis of an HIV/AIDS prevention programme targeting vulnerable groups in Benin. The AIDS-3 project (Projet Sida 3), a project targeting Female Sex Workers (FSWs), which was implemented from 2001 to 2005, is used as a case study to see how costs vary with location, volume of activities, and HIV prevalence rate. Activities and delivery modes were documented, and cost data have been collected both retrospectively (data on previous “Projet Sida 3” costs already available) and prospectively, using an ingredients-based costing methodology to consider both the financial and economic costs. Output measures were compiled directly from the intervention, and are related to the efficient delivery of different components of the intervention. Average cost per output or per outcome was estimated and cost variation within and between health centres over time was assessed. Results reveal that only the volume of activity is a prominent factor that affects the average cost. The location of the project and the experience of the staff also affect costs as well, but their significance is low. Field work activities that are more efficient in urban areas than in rural communities appear to be paramount in the fight against HIV as far as costs are concerned. / HIV/AIDS Cost analysis