The purpose of the present study was to evaluate the accuracy of the diagnosis of idiopathic pulmonary fibrosis (IPF) by respiratory physicians in six European countries, and to calculate the interobserver agreement between high-resolution computed tomography reviewers and histology reviewers in IPF diagnosis. The diagnosis of usual interstitial pneumonia (UIP) was assessed by a local investigator, following the American Thoracic Society/European Respiratory Society consensus statement, and confirmed when a minimum of two out of three expert reviewers from each expert panel agreed with the diagnosis. The level of agreement between readers within each expert panel was calculated by weighted kappa. The diagnosis of UIP was confirmed by the expert panels in 87.2% of cases. A total of 179 thoracic high-resolution computed tomography scans were independently reviewed, and an interobserver agreement of 0.40 was found. Open or thoracoscopic lung biopsy was performed in 97 patients, 82 of whom could be reviewed by the expert committee. The weighted kappa between histology readers was 0.30. It is concluded that, although the level of agreement between the readers within each panel was only fair to moderate, the overall accuracy of a clinical diagnosis of idiopathic pulmonary fibrosis in expert centres is good (87.2%).