The 8 histologic subtypes of IIP, in decreasing order of frequency, are Idiopathic pulmonary fibrosis (identified histologically as usual interstitial pneumonia) Desquamative interstitial pneumonia Nonspecific interstitial pneumonia Cryptogenic organizing pneumonia Respiratory bronchiolitis-associated interstitial lung disease (RBILD) Acute interstitial pneumonia Lymphocytic interstitial pneumonia Idiopathic pleuroparenchymal fibroelastosis These subtypes are characterized by varying degrees of interstitial inflammation and fibrosis (1).