Interstitial lung disease is not necessarily a major disease; it needs to be analysed on a disease-specific basis and there is no clear cut-off for major disease, so the prognosis is outlined. For interstitial lung disease with a known cause, the prognosis is generally fair and less life threatening as it can be improved with aggressive treatment. In contrast, there is often no effective treatment for interstitial lung disease of unknown etiology, particularly in idiopathic pulmonary fibrosis disease, which is difficult to cure, has a high mortality rate, and patients have a poor prognosis with a median survival of 2-3 years.