This report summarizes the latest data on the epidemiology of HIV. The epidemiological estimates reflect continued improvement in national HIV surveillance systems and estimation methodology. In 2007–2008, national household surveys with anonymous HIV testing components were conducted in 11 countries, including nine in sub-Saharan Africa. Improvements in HIV surveillance and information systems not only provide a clearer, more reliable picture of the epidemic at the global, regional and country levels but are also helping national governments and other stakeholders to tailor AIDS responses in order to maximize the impact on public health. The epidemic appears to have stabilized in most regions, although prevalence continues to increase in Eastern Europe and Central Asia and in other parts of Asia due to a high rate of new HIV infections. Sub-Saharan Africa remains the most heavily affected region, accounting for 71% of all new HIV infections in 2008. The resurgence of the epidemic among men who have sex with men in high-income countries is increasingly well-documented. Differences are apparent in all regions, with some national epidemics continuing to expand even as the overall regional HIV incidence stabilizes.