Objective: To make a retrospective analysis of lung biopsy samples obtained from patients diagnosed with chronic idiopathic interstitial pneumonia, as defined in the American Thoracic Society/European Respiratory Society classification system made public in 2000. Methods: Samples from 252 open-lung biopsies of patients with interstitial lung disease, all performed between 1977 and 1999, were reviewed, and 39 cases of idiopathic interstitial lung disease were selected and re-evaluated by two pathologists in accordance with the American Thoracic Society/European Respiratory Society classification system. Results: Among those 39 cases, the diagnoses were maintained in 28 (71.8%). A new pathologic entity, nonspecific interstitial pneumonia, was included in the reclassification, and overlapping patterns were observed in 6 cases. Of the 28 cases in which the diagnosis of chronic idiopathic interstitial pneumonia remained unchanged, idiopathic pulmonary fibrosis was accompanied by cryptogenic organizing pneumonia in 4, cryptogenic organizing pneumonia was accompanied by nonspecific interstitial pneumonia in 1, and desquamative interstitial pneumonia was accompanied by nonspecific interstitial pneumonia in 1. All cases of idiopathic pulmonary fibrosis were confirmed, although 3 of those were found to be accompanied by cryptogenic organizing pneumonia. Virtually all prior diagnoses were maintained in the review of the biopsy samples (p > 0,05). Conclusion: The American Thoracic Society/European Respiratory Society system of classifying interstitial lung disease is a useful tool for pathologists who deal with lung biopsies.

Keywords: Pulmonary fibrosis; Lung diseases, interstitial