PURPOSE: The purpose of this study was to evaluate the high-resolution CT(HRCT) appearance of abnormalities of small airways and lung parenchyma associated with bronchiectasis and to correlate HRCT appearance and the results of pulmonary function tests. MATERIALS AND METHODS: The author retrospectively reviewed medical recordsand HRCT scans of 33 patients with bronchiectasis. Abnormalities of small airways and lung parenchyma in lobeswith bronchiectasis were assessed on HRCT scan. The findings on HRCT were correlated with the results of pulmonary function tests in 20 patients. In two specimens obtained at lobectomy, histologic examinations were conducted to determine the pathologic basis for CT findings of disease of small airways. RESULTS: Patchy areas of low attenuation(n=27), centrilobular nodules or branching opacities(n=20), irregular hyper attenuation(n=16), and areasof ground-glass attenuation(n=4) were observed on HRCT scans. In the lobar evaluation, areas of low attenuation were observed in 66(76%) of the 87 lobes with bronchiectasis. Areas of low attenuation were also identified inseven(9%) of the 75 lobes without bronchiectasis. On expiratory HRCT, the lung parenchyma with areas of low attenuation did not show a normal increase in CT attenuation and remained more lucent than surrounding normallung, which suggested that air was trapped in the lung parenchyma. Of the 20 patients who underwent pulmonary function tests, six showed an obstructive pattern. These six had more lobes with bronchiectasis and with areas oflow attenuation than the other 14 patients, who did not have an obstructive pulmonary function pattern(p<.01). Intwo patients who had undergone lobectomy, pathologic examination showed bronchiolities obliterans in small airway speripheral to the dilated bronchi. CONCLUSION: In bronchiectasis, areas of low attenuation and centrilobular nodules or branching opacities are commonly observed in the lung parenchyma peripheral to the dilated bronchi on HRCT. These HRCT findings correspond pathologically to bronchiolitis obliterans and to lung parenchyma with trapped air. The number of loves with bronchiectasis and with areas of low attenuation correlate significantly with an obstructive pattern on pulmonary function tests.