PURPOSE: To assess the high-resolution CT (HRCT) findings of small airway abnormalities after mycoplasma pneumonia and correlate them with the findings of chest radiography performed during the acute and follow-up phases of the condition. MATERIALS AND METHODS: We retrospectively evaluated HRCT and chest radiographic findings of 18 patients with clinical diagnosis of small airway disease after mycoplasma pneumonia (M:F=8:10, mean age: 8.3 years, mean time interval after the initial infection; 26 months). We evaluated the lung parenchymal and bronchial abnormalities on HRCT (n=18). In addition, presence of air-trapping was assessed on expiratory scans (n=13). The findings of HRCT were correlated with those of chest radiography performed during the acute phase of initial infection (n=15) and at the time of CT examination (n=18), respectively. RESULTS: HRCT revealed lung parenchymal abnormalities in 13 patients (72%). A mosaic pattern of lung attenuation was noted in ten patients (10/18, 56%), and air-trapping on expiratory scans was observed in nine (9/13, 69%). In nine of 14 (64%) with negative findings at follow-up chest radiography, one or both of the above parenchymal abnormalities was observed at HRCT. In four patients (27%), parenchymal abnormalities were seen at HRCT in areas considered normal at acute-phase chest radiography. Bronchiectasis or ateclectasis was observed in eight (44%) and four (22%) patients, respectively, at HRCT. The CT features of Swyer-James syndrome such as a unilateral hyperlucent lung with reduced lung volume and attenuated vessels were noted in two patients (11%). CONCLUSION: HRCT can clearly demonstrate lung parenchymal and bronchial abnormalities of small airway disease after mycoplasma pneumonia in children.