BACKGROUND: Since 2003, the President's Emergency Plan for AIDS Relief (PEPFAR) has been the most ambitious initiative to address the global HIV epidemic. However, the effect of PEPFAR on HIV-related outcomes is unknown. OBJECTIVE: To assess the effect of PEPFAR on HIV-related deaths, the number of people living with HIV, and HIV prevalence in sub-Saharan Africa. DESIGN: Comparison of trends before and after the initiation of PEPFAR's activities. SETTING: 12 African focus countries and 29 control countries with a generalized HIV epidemic from 1997 to 2007 (451 country-year observations). INTERVENTION: A 5-year, $15 billion program for HIV treatment, prevention, and care that started in late 2003. MEASUREMENTS: HIV-related deaths, the number of people living with HIV, and HIV prevalence. RESULTS: Between 2004 and 2007, the difference in the annual change in the number of HIV-related deaths was 10.5% lower in the focus countries than in the control countries (P = 0.001). The difference in trends between the groups before 2003 was not significant. The annual growth in the number of people living with HIV was 3.7% slower in the focus countries than in the control countries from 1997 to 2002 (P = 0.05), but during PEPFAR's activities, the difference was no longer significant. The difference in the change in HIV prevalence did not significantly differ throughout the study period. These estimates were stable after sensitivity analysis. LIMITATION: The selection of the focus countries was not random, which limits the generalizability of the results. CONCLUSION: After 4 years of PEPFAR activity, HIV-related deaths decreased in sub-Saharan African focus countries compared with control countries, but trends in adult prevalence did not differ. Assessment of epidemiologic effectiveness should be part of PEPFAR's evaluation programs. PRIMARY FUNDING SOURCE: Agency for Healthcare Research and Quality.