Background and AimsPrevious studies mostly focused on the diagnostic accuracy of transbronchoscopic lung biopsy (TBLB) in the diagnosis of interstitial lung diseases (ILDs). We aimed to explore the clinical usefulness of TBLB results in the diagnostic procedure of undefined ILDs. MethodsThe retrospective analysis included patients undergoing TBLB for the diagnosis of undefined ILDs from January 2007 to December 2010. The clinically useful TBLB was defined as that lead to a specific histopathological diagnosis or that was consistent with the working diagnosis based on existing clinical and radiological data. ResultsA total of 664 patients were included in the study. TBLB failed to obtain lung parenchyma in 155 cases (23.3%). TBLB was considered clinically helpful in 202 procedures (30.4%), including 114 cases that provided definitive histopathological diagnoses and 88 cases that were consistent with working diagnoses. Among 202 cases of clinically useful TBLBs, the majority were diagnosed as pulmonary alveolar proteinosis (PAP) (67 cases, 33.2%), connective tissue disease-related ILDs (CTD-ILDs) (65, 32.2%) and idiopathic pulmonary fibrosis (IPF) (33, 16.3%). Although TBLB could provide definitive histopathological diagnoses in all cases diagnosed as PAP, only few cases of IPF (7, 21.2% of IPF diagnoses) and CTD-ILDs (9, 13.8% of CTD-ILD diagnoses) could be identified by TBLBs. ConclusionThe clinical usefulness of TBLB, in conjunction with thorough clinical and radiological data, in the diagnosis of ILDs may be varied depending on different subtypes. The use of histopathological analysis and the type of biopsy employed should therefore be considered on a case-by-case basis.