Open lung biopsy was performed in thirty patients for the diagnosis and staging evaluation of interstitial lung disease during the period from January 1987 until December 1992. The age of the patients ranged from 14 to 71 years [mean 48 years], and the patients consisted of 14 males and 16 females. Preoperative FEV1`s were from 0.80 liter to 3.88 liters [mean 1.66]. Other non-invasive diagnostic studies such as PCNA, bronchoalveolar lavage, TBLB, and gallium scan were also done in addition to X-ray and high-resolution chest CT. Tweaty-eight were correctly diagnosed and 2 cases were not [diagnostic yield rate 93.3%]. Among the 28 cases,pathologic diagnosis influenced further treatment regimens and prognostic expectations in 23 cases [82.1%]. The diagnostic non-invasive studies other than open lung biopsy yielded a correct diagnosis without staging only in 5 cases. There was no mortality and only one complication, ARDS ; however, the patient recovered after 5 days ventilator support. Open lung biopsy, which is the gold standard for the diagnosis and staging evaluation of interstitial lung disease can be done safely and has value in clinical decision making. Also knowledge of the involvement of the lesion is important for proper selection of the biopsy site.