OBJECTIVES: Economists and epidemiologists from 10 countries in Latin America and the Caribbean (LAC) reviewed the methods used to develop estimates for resource requirements to address HIV/AIDS prevention and care in low- and middle-income countries. METHODS: They applied their country-specific knowledge to re-estimate the costs, coverage, and capacity of their health and education systems to expand HIV/AIDS interventions by 2005. A discrepancy of 173 million US dollars exists between the model estimates and those of country specialists. RESULTS: The most important difference between the model estimates and those of country specialists was in the estimated future price of highly active antiretroviral therapy. To a large extent, the estimates of the model reflect the efficiency gains that could result from purchasing arrangements that lead LAC countries to lower prices for antiretroviral drugs. CONCLUSION: This preliminary exercise with 10 LAC countries confirmed the validity of the use of these estimates as tools at the international level, given current data limitations, both to guide the allocation of resources across diseases and countries, and for advocacy and resource mobilization. In addition, with the country revisions, these estimates have also been shown to be key tools for country-level strategic planning.