In Chad, as in most sub-Saharan Africa countries, HIV/AIDS poses a massive public health threat as well as an economic burden, with prevalence rates estimated at 9% of the adult population. In defining and readjusting the scope and content of the national HIV/AIDS control activities, policy makers sought to identify the most cost-effective options for HIV/AIDS control. The cost-effectiveness analysis reported in this paper uses a mixture of local and international information sources combined with appropriate assumptions to model the cost-effectiveness of feasible HIV prevention options in Chad, with estimates of the budget impact. The most cost-effective options at under US$100 per infection prevented were peer group education of sex workers and screening of blood donors to identify infected blood before transfusion. These options were followed by mass media and peer group education of high risk men and young people, at around US$500 per infection prevented. Anti-retroviral therapy for HIV infected pregnant women and voluntary counselling and testing were in the order of US$1000 per infection prevented. The paper concludes with recommendations for which activities should be given priority in the next phase of the national HIV/AIDS control programme in Chad.