Objective: To investigate the role of CT scanning in diagnosing severe acute respiratory syndrome (SARS).Methods: One hundred and twelve times of spiral CT scanning, 106 times on the chest with standard pulmonary and mediastinal window, 5 on the brain and once on the abdomen, were performed in 82 patients (37 males and 45 females) of SARS.Results: Bilateral shadows showed in 66 patients (80.48%) and unilateral shadow in 16 (19.52%). The lung CT findings were sub-pleural focal consolidation in 26 patients (31.70%), flaky cloudy opacity in 53 (64.63%), large area consolidation in 9 (10.97%), ground-glass blurry shadow in 31 (37.80%), alveolar substantive shadow in 14 (17.07%) and interstitial changes in 16 (19.51%). The pulmonary CT signs of SARS were relatively characterized by: (1) The lesions tending to multiply occur, mostly to be bilaterally distributed and commonly involved in the lower lung field. (2) The lung shadows mostly showed as sub-pleural focal consolidation, flaky cloudy shadow, large area consolidation, ground-glass blurry shadow, and often accompanied with signs of broncho-inflation. (3) Having opacified nodular shadows in the alveolar cavities. (4) Rapid progressions or changes on the size, amount, and distribution of the lesions likely to be found in dynamic observation of chest X-ray and CT scanning, i.e., markedly dynamic changes found within 24 to 48 hrs. Lesions with these characteristics may be recognized as pulmonary changes possibly induced by SARS. Complications were found in 6 patients (7.31%), including tuberculosis of lung and brain accompanied with pneumomediastinum in one patient, secondary infection of lung in 2, pneumothorax in 1, pulmonary fungus in 1, and pyothorax in 1.Conclusion: CT scanning is a sensitive method for diagnosis of SARS, by which more accurate assessment of the abnormal changes of lung and occurrence of complications in SARS patients can be made.