Objective To study the chest X ray image features of patients with severe SARS Methods Chest X ray image features in 36 patients with severe SARS were retrospectively analyzed The image characteristics were compared with those of 224 patients with common SARS Results The important chest X ray imaging features of 36 patients with severe SARS included small patch of infiltration (n=27, 75 0%), large patch of infiltration (n=22, 61 1%), large area of lung consolidation (n=10, 27 3%), interstitial lung lesion (n=26, 72 2%), ground glass shadow (n=28, 77 8%), irregular linear opacity (n=15, 41 7%), diffuse lung lesion (n=12, 33 3%), with single lung involved (n=9, 25 0%), and both lungs involved (n=32, 88 9%) The rates of large patch of infiltration, large area of lung consolidation, ground glass shadow, diffuse lung lesion and involvement of both lungs in patients with severe SARS were significantly higher than those in patients with common type of SARS (all P <0 01) Out of the 11 severe SARS patients who died, nine had large area of ground glass shadow with air bronchogram in both lungs before death Conclusions Large patch of infiltration, large area of consolidation, ground glass shadow, diffuse lung lesion and involvement of both lungs were the main X ray image characteristics of patients with severe SARS Large area of ground glass shadow with air bronchogram in both lungs indicated a bad prognosis Objective To study the chest X ray image features of patients with severe SARS Methods Chest X ray image features in 36 patients with severe SARS were retrospectively analyzed The image characteristics were compared with those of 224 patients with common SARS Results The important chest X ray imaging features of 36 patients with severe SARS included small patch of infiltration (n = 27, 75 0%), large patch of infiltration (n = 22, 61 1%), large area of ​​lung consolidation interstitial lung lesion (n = 26, 72 2%), ground glass shadow (n = 28,777%), irregular linear opacity (n = 15, 41 7% ), with single lung involvement (n = 9, 25%), and both lungs involved (n = 32, 88 9%) The rates of large patch of infiltration, large area of ​​lung consolidation, ground glass shadow, diffuse lung lesion and involvement of both lungs in patients with severe SARS were significantly higher than those in patients with common type of SARS (all P <0 01) Out of the 11 severe SARS patients who died, nine had large area of ​​ground glass shadow with air bronchogram in both lungs before death Conclusions Large patch of infiltration, large area of ​​consolidation, ground glass shadow, diffuse lung lesion and involvement of both lungs were the main X ray image characteristics of patients with severe SARS Large area of ​​ground glass shadow with air bronchogram in both lungs indicating a bad prognosis