Summary: The usefulness of thin-section computed tomography (CT) in the identification of the specific and clinically relevant pathologic changes in airway disease has been well documented. However, this approach has not been used for objective evaluation in patients with diffuse panbronchiolitis. Therefore attempts were made to use it in patients with diffuse panbronchiolitis. The study group included 12 men and 10 women, 17 to 69 years of age (mean, 47 years) with diffuse panbronchiolitis. All patients were evaluated by thin-section CT and pulmonary function testing. The CT score was calculated by a modified score criteria. The correlations between the CT score and the pulmonary function parameters were assessed by Pearson's linar regression analysis. Bronchiolar inflammation and airway-ectasia were present in all 22 patients. Periairway thickening was present in 17 patients. Pus plugging was present in 18 patients. Two patients had bullae formation, and 6 had air-trapping. Pulmonary collapse or consolidation was evident in 6patients. The CT score demonstrated a significant negative correlation with FEV1% (r=-3.267, p=.0230), %VC (r=-4.658, p=.0018), and arterial blood oxygen concentration (r=-1.009, p=.0381). The thin-section CT findings in patients with diffuse panbronchiolitis closely resembled those in patients with cystic fibrosis, previously described. Furthermore, a CT scoring system is useful for objective evaluation of lung disease severity in patients with diffuse panbronchiolitis.