As more effective HIV therapies have become available, resource constraints and cost-effectiveness have increasingly been at the centre of the debate on HIV care. Economic analysis is an important methodological approach to the understanding and establishment of priorities for health interventions designed to combat HIV in both high-income and low-income countries. In this paper, I briefly discuss different types of clinical economic analysis, and then consider the cost, affordability and cost-effectiveness of combination antiretroviral therapy in HIV patients in high-income and low-income countries. In high-income countries, HIV disease has become an expensive treatable chronic disease, with annual expenditures per patient of about US$ 20 000. Cost-effectiveness analyses show that antiretroviral therapeutic regimens offer good value for the resources spent compared to many other accepted health care interventions. In low-income countries, major programmes of combination antiretroviral therapy distribution are being planned and becoming operational as drug prices plummet and resources increase. More refined cost-effectiveness analyses are needed to evaluate available HIV/AIDS prevention, treatment, and care, and to identify the interventions that provide the best value for money.