Abstract： Objective To evaluate chest radiographic findings of children with 2009 influenza ( H1N1 ) virus infection. Method Data of 235 patients who had microbiologically confirmed H1N1 infection and available chest radiograph obtained between May 1st 2009 and Jan. 31st 2010 were retrospectively analyzed. The final study group was divided on the basis of clinical course [group 1 mild, outpatients without hospitalization ( n = 172 ); group 2 moderate, inpatients with brief hospitalization ( n = 49 ); group 3 severe, ICU admission (n = 14)]. Four pediatric radiologists reviewed all the chest radiographs of lung parenchyma, airway, pleural abnormalities and also anatomic distribution of the disease. Result No significant sex or age differences were found among the study groups ( P ＞0.05 ). The mean interval between the onset of clinical symptom and the initial chest radiography was (5.91 ± 1. 64) days (group 1 ), (3.60 ±1.43 ) days ( group 2) and ( 1.21 ± 0.41 ) days ( group 3 ), respectively. The differences among the three groups were significant statistically ( χ2 = 13.368, P ＜ 0.01 ). The ratio of abnormality presented at initial chest X-ray was 79.7% in group 1,91.8% in group 2 and 100% in group 3. Radiographically, there were prominent peribronchial markings ( group 1, 55.2%; group 2, 83.7%; and group 3, 78.6% ),consolidation ( group 1, 34.3%; group 2, 69.4%; and group 3, 100.0% ), hyperinflation ( group 1,22.1%; group 2, 44.9%; and group 3, 50.0% ) and ground glass opacity ( group 1, 0.6%; group 2,2.0%; and group 3, 14.3% ) in the chest radiographs. The differences of presenting were statistically significant (P ＜0.01 ). In the severe group, the lesions distributed diffusely and asymmetrically with multi lobe involvements. Conclusion In children with 2009 influenza A H1N1 viral infection, the interval between the onset of clinical symptom and initial chest radiography, the ratio of abnormality presented at initial chest X-ray film and the severity of chest film are parallel to their clinical situation.