The classification of interstitial pneumonia with autoimmune features (IPAF) is used to categorize patients with an autoimmune substrate and pulmonary interstitial involvement, who do not meet the classification criteria for any specific connective tissue disease. These patients seem to have a better clinical course than patients with IPAF. The diagnosis of IPAF is of paramount importance and to identify and to treat forms of early onset of pulmonary interstitial disease without any established damage and to recognize incomplete forms of connective diseases preventing complete clinical manifestation.