This article examines the international response to AIDS from a fiscal perspective: first the financing of the international response to AIDS, especially the role of external financing, and second, a more comprehensive perspective on the costs of the national response to AIDS relevant for fiscal policy. The second half of the article focuses on the effectiveness of the response to AIDS. We find that there is little basis for concerns about macroeconomic constraints to scaling up, in light of the moderate scale of AIDS-related aid flows relative to overall aid. Regarding sectoral constraints, the picture is more differentiated. Many countries with high prevalence rates have also achieved high rates of access to treatment, but most of these are middle-income countries. Our econometric analysis credits external aid as a key factor that has enabled higher-prevalence countries to cope with the additional demands for health services. At the same time, gross domestic product per capita and health sector capacities are important determinants of access to treatment.