PURPOSE: To evaluate late lung parenchymal change, as seen on high-resolution CT(HRCT) in children with mycoplasma pneumonia MATERIALS AND METHODS: Twenty-three patients [15 boys and 8 girls aged two to 13 (mean, 6) years] with mycoplasma pneumonia underwent HRCT four to 39 (mean, 10) months after initial infection. Using increased mycoplasma antibody titer(> 1:640) mycoplasma pneumonia was diagnosed, and patients were divided into two groups : high titer group (antibody titer>1: 5120), and lower titer group (<1:5120). CT scans were performed using 2mm collimation and 5-10mm interval from apex to diaphragm. In seven patients who were cooperative, both inspiratory and expiratory scans were obtained at a window width of 1600 HU and level of -700. HRCT findings of mosaic low attenuations and changes in bronchioles and bronchial walls were assessed by three radiologists and correlated with initial chest radiographic findings. RESULTS: On HRCT, 17 of 23 patients (74 %) demonstrated abnormal findings. These included mosaic attenuation of lung density alone in 11 of 17 patients (65%), mosaic attenuation associated with bronchiectasis in five ( 29 %), and bronchiectasis only in one (6 %). Mosaic attenuation was more accentuated on expiratory scans than on inspiratory. These findings were obtained in 10 of 12 high titer group and in 7 of 11 in the lower titer group. In 15 of 23 patients (65 %), involved ageas seen on HRCT exactly corresponded with initially involved areas seen on chest radiographs (CXR). Two patients in whom findings on initial CXR were normal showed mosaic attenuation on HRCT. Six patients in whom such findings were abnormal showed normal findings on HRCT, a fact which reflected their complete recovery. CONCLUSION: The most common late parenchymal change in mycoplasma pneumonia, as seen on HRCT, was mosaic attenuation of lung density followed by bronchiectasis. The latter is presumably due to bronchiolitis obliterans, a well-known complication. We believe that HRCT is very useful for the evaluation of long-term sequelae of mycoplasma pneumonia in children.