Additional funding recently became available to help resource-constrained countries scale up their HIV treatment and prevention activities. This increased funding is accompanied by an increased demand for accountability from stakeholders. Many countries will need to make substantial improvements in their current HIV surveillance methods to monitor the collective national impact of these treatment and prevention initiatives. However, whereas most resource-constrained countries have monitored the prevalence of HIV, they have collected little information on other events in the HIV disease process, such as HIV incidence, rate of HIV drug resistance, number of deaths due to AIDS and only modest emphasis has been placed on AIDS reporting in generalized epidemics, resulting in severe underreporting. In addition, data on mortality trends are often not gathered. Furthermore, less than half of the countries with low-level/concentrated epidemics have tailored their surveillance systems to the local epidemic, behavioral surveillance is often not present, an integrated analysis of data is not widespread, and data are rarely used to inform policy. In January 2004, a conference was convened in Addis Ababa, Ethiopia, to examine new strategies for surveillance in resource-constrained countries, and their use in monitoring and evaluating HIV activities. This supplement summarizes the newest approaches and lessons learned for HIV/AIDS surveillance, based on presentations and discussions from that conference. This article provides an overview of HIV/AIDS surveillance in resource-constrained settings and discusses the history, current approaches, and future directions for HIV/AIDS surveillance in generalized and low-level/concentrated epidemics.