PURPOSE: To evaluate and compare the high-resolution computed tomography (HRCT) findings of patients with H1N1 influenza-associated pneumonia compared usual community acquired pneumonia (CAP), to determine whether there were any useful common HRCT findings predicting their prognosis. MATERIALS AND METHODS: HRCT findings of 31 patients (M:F=16:15, mean age 42 yrs) with Influenza A (H1N1) infection were retrospectively reviewed for abnormal HRCT findings and compared to HRCT findings of CAP in matched patients. Patients were matched according to age and sex, from 2009 to January 2010. RESULTS: The predominant HRCT findings of pneumonia consisted of areas of consolidation and/or ground-glass opacity (GGO) which showed no statistically significant differences when comparing the two groups. However, the abnormalities of H1N1-related pneumonia showed higher bilaterality and multilobar or multisegmental involvement compared with CAP (p<0.05). Internal low attenuation or air-densities in pulmonary infiltration /or lymphadenopathy was observed only in patients with CAP (p<0.05). HRCT findings in 8 patients with poor clinical outcome had bilaterality (p=0.015), multilobar, and multisegmental involvement. CONCLUSION: The predominant HRCT findings of H1N1-related pneumonia were areas of consolidation and/or GGO. In addition, H1N1-related pneumonia showed higher bilaterality or multilobar/multisegmental involvement compared with CAP. The patients who presented bilaterality had a worse clinical outcome.