Retrospective review of 26 patients undergoing open lung biopsy at the Yonsei University during 10 years period was conducted to evaluate open lung biopsy for DILD. From January 1980 to August 1990, open lung biopsy was performed in 26 patients through a limited thoracotomy incision[a limited anterior or a posterolateral thoracotomy]. Open lung biopsy was indicated for diffuse interstitial pulmonary diseases undiagnosed by indirect clinical and radiological diagnostic methods. The types of incision were limited anterior[11] and limited posterolateral[15]. Preoperative evaluation of the lung disease included sputum culture[26], sputum cytology [19], bronchoscopy[9] and TBLB[7]. In 23 patients the histologic appearances after open lung biopsy were sufficiently specific histologic pictures to confirm diagnosis. The results of the biopsies changed usual therapeutic plan in 17 patients among them. The complications were resp. insufficiency[3], pulmonary ed6ma[3], sepsis[2], and others[3] in 6 patients. Diagnosis from the open lung biopsy was included respiratory pneumonia[7], fibrosis[7], infection[5], malignancy[2], others[5]. 4 patients died of respiratory insufficiency. The causes of the other three death were not due to direct result of the biopsy itself. Open lung biopsy in the patient with a diffuse infiltrative lung disease is an one of the accurate diagnostic method and frequently leads to change of the therapeutic plans. So we conclude that open lung biopsy remains our diagnostic method of choice in diffuse infiltrative lung disease undetermined etiology.