Currently, five types of interstitial pneumonia of unknown etiology or IIP have been described; DAD, UIP, BOOP, DIP and LIP. A summary of the features of clinical course, prognosis and therapeutic effects to steroid hormone treatment of the five types of interstitial pneumonia of unknown etiology or IIP is given in Table 15). Among the previous mentioned 52 open lung biopsy cases of interstitial pneumonia of unknown etiology or IIP, for which an open lung biopsy was necessary for diagnosis, the majority of those cases (81%) was IPF (UIP) while idiopathic BOOP occurred as the second in frequency (13%). These data will help in understanding the clinical outcome and the therapeutic response to steroid hormone treatment in cases of interstitial pneumonia of unknown etiology or IIP, because idopathic UIP is slowly progressive and usually not responsive to steroid while idiopathic BOOP is usually responsive to steroid hormone treatment and may regress even spontaneously. Cases of IPF (UIP) should have revolutional modalities for therapy.