This study reports the clinical, radiologic, and laboratory features of 10 epidemiologically linked patients with severe acute respiratory syndrome (SARS) in Hong Kong between February 22 and March 22, 2003. The patients, all from southern China, presented with fever, rigor, dry cough, dyspnea, malaise, headache, and hypoxemia. The incubation period ranged from 2 to 11 days. Chest radiographs showed progressive air-space disease, and two patients died of respiratory failure. Microbiologic tests did not identify Mycoplasma pneumoniae, Chlamydia pneumoniae, or Legionella pneumophila as the cause. Empirical treatment with corticosteroids and ribavirin was effective, with most patients showing clinical and radiographic improvement. The study emphasizes the contagious nature of SARS and the importance of isolation precautions for healthcare workers. The exact microbiology of SARS remains unresolved, but the clinical and radiographic features suggest a viral cause.This study reports the clinical, radiologic, and laboratory features of 10 epidemiologically linked patients with severe acute respiratory syndrome (SARS) in Hong Kong between February 22 and March 22, 2003. The patients, all from southern China, presented with fever, rigor, dry cough, dyspnea, malaise, headache, and hypoxemia. The incubation period ranged from 2 to 11 days. Chest radiographs showed progressive air-space disease, and two patients died of respiratory failure. Microbiologic tests did not identify Mycoplasma pneumoniae, Chlamydia pneumoniae, or Legionella pneumophila as the cause. Empirical treatment with corticosteroids and ribavirin was effective, with most patients showing clinical and radiographic improvement. The study emphasizes the contagious nature of SARS and the importance of isolation precautions for healthcare workers. The exact microbiology of SARS remains unresolved, but the clinical and radiographic features suggest a viral cause.