The AIDS pandemic is a human tragedy that is threatening development in the poorest countries. There is no cure or vaccine, but the tools to control the epidemic already exist. Nevertheless, there are few examples of national AIDS control programmes that have had an impact on the epidemic. We (an economist and a planner) attribute this to the reluctance of governments to confront AIDS and a failure to prioritise activities in the face of severe financial and administrative constraints. When implementation capacity is weak, expanding the number of activities may not improve programme effectiveness. Rather, by implementing a smaller, core set of the most cost-effective activities on a national scale, policymakers could have a huge effect on the overall epidemic in a sustained way and provide a foundation for expansion. We propose three core priorities for AIDS control in poor countries for prevention, treatment, and mitigation of the impact.