In the present study, chest radiographs were abnormal in two of 18 patients with H1N1, which was less frequent than that of a previous report, which showed a 42% rate of chest radiograph abnormality (12) . This suggests that negative findings on chest radiographs cannot rule out the possibility of the pandemic H1N1 2009 influenza virus infection, particularly in its early stage or for an uncomplicated influenza infection (14) . Thin-section CT examination results revealed that abnormal findings were found in six out of 12 patients (50%). The most common CT abnormalities included small GGOs in five out of six patients and nodules in all six patients. However, in the previous studies (12, 13) , multifocal consolidations (two of seven patients and 50%) and GGOs (two of seven patients and 25%) were the most common CT findings of the pandemic H1N1 2009 influenza virus infection. The differences between the present study and previous studies could be attributed to the fact that radiological examinations in the present study were performed at the initial presentation, and probably the early stages of the disease; whereas in previous studies (12, 13) , radiological examinations were performed at various times after symptom onset.