As funding mechanisms like the Global Fund for HIV/AIDS, Tuberculosis and Malaria increasingly make funding decisions on the basis of burden of disease estimates and financial need calculations, the importance of reliable and comparable estimating methods is growing. This paper presents a model for estimating HIV/AIDS health care resource needs in low- and middle-income countries. The model presented was the basis for the United Nations' call for US dollars 9.2 billion to address HIV/AIDS in developing countries by 2005 with US dollars 4.4 billion to address HIV/AIDS health care and the rest to deal with HIV/AIDS prevention. The model has since been updated and extended to produce estimates for 2007. This paper details the methods and assumptions used to estimate HIV/AIDS health care financial needs and it discusses the limitations and data needs for this model.