Definitive diagnosis requires a surgical lung biopsy demonstrating a usual interstitial pneumonia pattern plus exclusion of other causes of interstitial lung disease, abnormal pulmonary function demonstrating restriction and/or impaired gas exchange, and abnormalities of CXR or high-resolution CT consistent with pulmonary fibrosis.

The diagnosis can also be made in the absence of surgical lung biopsy if major and minor clinical criteria are met, including appropriate historic features, pulmonary function abnormalities, classic CT findings, and a negative evaluation for other causes of pulmonary fibrosis.