[2] Examples of known causes of UIP include connective tissue diseases (primarily rheumatoid arthritis), drug toxicity, chronic hypersensitivity pneumonitis, asbestosis and Hermansky–Pudlak syndrome.

[2] UIP may be diagnosed by a radiologist using computed tomography (CT) scan of the chest, or by a pathologist using tissue obtained by a lung biopsy.

Radiologically, the main feature required for a confident diagnosis of UIP is honeycomb change in the periphery and the lower portions (bases) of the lungs.

The histologic hallmarks of UIP, as seen in lung tissue under a microscope by a pathologist, are interstitial fibrosis in a "patchwork pattern", honeycomb change and fibroblast foci (see images below).

[citation needed] Some patients do well for a prolonged period of time, but then deteriorate rapidly because of a superimposed acute illness (so-called "accelerated UIP").