RATIONALE: The level diagnostic likelihood at which physicians prescribe antifibrotic therapy without requesting surgical lung biopsy (SLB) in patients suspected of idiopathic pulmonary fibrosis (IPF) is unknown. OBJECTIVES: To determine how often physicians advocate SLB in patient sub-groups defined by IPF likelihood and risk associated with SLB and to identify the level of diagnostic likelihood at which physicians prescribe antifibrotic therapy with requesting SLB. METHODS: An international cohort of respiratory physicians evaluated 60 cases of interstitial lung disease, giving 1) differential diagnoses with diagnostic likelihood, 2) a decision on the need for SLB and, 3) initial management. Diagnoses were stratified according to diagnostic likelihood bands described by Ryerson el al. MEASUREMENTS AND MAIN RESULTS: 404 physicians evaluated the 60 cases (24,240 physician-patient evaluations). IPF was part of the differential diagnosis in 9,958/24,240 (41.1%) of all physician-patient evaluations. SLB was requested in 8.1%, 29.6% and 48.4% of definite, provisional high confidence and provisional low confidence diagnoses of IPF respectively. In 63.0% of provisional high confidence IPF diagnoses (70-89% likelihood), antifibrotic therapy was prescribed without requesting SLB. No significant mortality difference was observed between cases given a definite diagnosis of IPF (90-100% likelihood) and cases given a provisional high confidence diagnosis of IPF (HR 0.97, p=0.348, 95% CI 0.90-1.04). CONCLUSIONS: Most respiratory physicians prescribe antifibrotic therapy without requesting a SLB if a provisional high confidence diagnosis or "working diagnosis" of IPF can be made (likelihood>=70%). SLB is recommended in only a minority of patients with suspected but not definite IPF.