OBJECTIVE. The purpose of this study was to compare clinical and chest CT findings in patients with influenza A (H1N1) pneumonia and coronavirus disease (COVID-19) pneumonia. MATERIALS AND METHODS. Thirty patients with diagnosed influenza A (H1N1) virus infection (group A) and 30 patients with diagnosed COVID-19 (group B) were retrospectively enrolled in the present study. The clinical characteristics and chest CT findings of the two groups were compared. RESULTS. Fever, cough, expectoration, and dyspnea were the main symptoms in both groups with viral pneumonia, with cough and expectoration more frequently found in group A. Lymphopenia, an elevated C-reactive protein level, and an increased erythrocyte sedimentation rate were common laboratory test findings in the two groups. The median time from symptom onset to CT in group A and group B was 6 and 15 days, respectively, and the median total CT score of the pulmonary lobes involved was 6 and 13, respectively. Linear opacification, crazy-paving sign, vascular enlargement, were more common in group B. In contrast, bronchiectasis and pleural effusion were more common in group A. Other common CT features, including peripheral or peribronchovascular distribution, ground-glass opacities (GGOs), consolidation, subpleural line, air bronchogram, and bronchial distortion, did not show statistical significance. CONCLUSION. On CT, the significant differences between influenza A (H1N1) pneumonia and COVID-19 pneumonia were findings of linear opacification, crazy-paving sign, vascular enlargement, pleural thickening, and pleural effusion, which were more common in patients with COVID-19 pneumonia, and bronchiectasis and pleural effusion, which were more common in patients with influenza A (H1N1) pneumonia. Other imaging findings, including peripheral or peribronchovascular distribution, ground-glass opacities (GGO), consolidation, subpleural line, air bronchogram, and bronchial distortion, were not significantly different between the two patient groups.