An international outbreak of severe acute respiratory syndrome (SARS), a recently recognized syndrome caused by the newly identified severe acute respiratory syndrome-associated coronavirus (SARS-CoV), began in November 2002 and ended in July 2003. Coronavirus is a family of enveloped, single stranded-RNA viruses causing disease in humans and animals, but the other known coronaviruses that affect humans cause only the common cold. The number of SARS cases in 2003 was approximately 8000 across the world. Many recent studies have reinforced initial impressions that SARS-CoV is primarily transported via contact and/or droplets and that the combination of standard, contact, and droplet precautions is generally effective for its control. Active surveillance for clusters of cases of severe respiratory disease must be a first priority, especially among health care workers. Such surveillance should include the rapid diagnosis and prevention of other respiratory viruses that cause outbreaks of febrile respiratory disease-notably, influenza. Surveillance on the part of clinicians is the key to the early detection of any reemergence before it regains a foothold in the community. During the outbreak of SARS, ribavirin, steroids, interferon, convalescent plasma, and lopinavir/ itonavir were used in varying doses and combinations in different regions of the world. At present no definitive conclusions regarding the efficacy of any of these treatments can be drawn. New findings regarding SARS are continuing to be discovered at an unprecedented pace, permitting a better understanding of the disease and enabling better preparation for its possible returns. (Korean J Clin Microbiol 2005;8(2):105-112)