Severe acute respiratory syndrome (SARS) emerged in southern China in November 2002 and spread rapidly along international air routes in early 2003. Asian countries had the most cases (7,782) and deaths (729). SARS challenged Asian health care systems, disrupted Asian economies, and tested the effectiveness of the International Health Regulations. GAO was asked to examine the roles of the World Health Organization (WHO), the U.S. government, and Asian governments (China, Hong Kong, and Taiwan) in responding to SARS; the estimated economic impact of SARS in Asia; and efforts to update the International Health Regulations.