Severe acute respiratory syndrome, or SARS, was the first emerging infection of the 21stcentury. Severe pneumonia is the main symptom, and the case fatality rate was about 10%. In general, convalescence becomes less satisfactory with the age of the patient. The older the patient is, the more unsatisfactorily his or her convalescence is. The disease is transmitted mainly through the spread of droplets from the human respiratory tract. Many health care professionals became infected with SARS within the medical facilities in which they worked. No peculiar medicine or vaccine for SARS has yet been developed. A worldwide epidemic of SARS centered in China broke out around during the period from 2002 to 2003; about 8,000 cases were recorded. Although this epidemic has come to an end, attention should be paid to SARS because of its possible reemergence. Preparedness for SARS can be also applied to measures against other emerging infections.