Abstract: Purpose : To retrospectively evaluate the radiographic appearances and pattern of progression of severe acute respiratory syndrome (SARS). Materials and methods : Chest radiographs obtained at clinical presentation and during treatment in 22 patients with confirmed SARS (8 men, 14 women; mean age, 39。9 years; age range, 14-73 years) were assessed. Radiographic appearances of pulmonary parenchymal abnormality, distribution, and extent of involvement on initial chest radiographs were documented. Recognizable patterns of radiographic progression were determined by comparing the overall mean percentage of lung involvement for each patient on serial radiographs. Results: Initial chest radiographs were abnormal in 19 of 22 patients and showed air-space opacity. Lower lung zone (15 of 22) were more commonly involved. In most patients, peripheral lung involvement was more common (15 of22). Unifocal involvement (19of 22) was more common than multifocal or bilateral involvement. No cavitation, lymphadenopathy, or pleural effusion was demonstrated. Initial focal air-space opacity in 14 of 22 patients progressed to unilateral multifocal or bilateral involvement during treatment. Conclusion : Predominant peripheral location; common progression pattern from unilateral focal air-space opacity to unilateral multifocal or bilateral involvement during treatment; and lack of cavitation, lymphadenopathy, and pleural effusion are the more distinctive radiographic findings of SARS.