BACKGROUND & METHOD: Bronchiolitis obliterans organizing pneumonia(BOOP) is a specific clinicopathologic condition characterized by chronic inflammatory interstitial infiltrates. Cryptogenic form of BOOP presents subacute clinical course of flu-like illness, such as cough, fever, dyspnea with exertion and other constitutional symptoms. Pathologically it shows the presence of granulation tissue filling the lumen of terminal and respiratory bronchioles, extending into distal airspaces. Recently, we reviewed 24 cases of idiopathic type of BOOP, 5 cases of our hospital and another 19 cases on Korean literatures, and compared with reviewed data from foreign literatures. RESULTS: Mean age was 54 years old and there was female preponderance in domestic reports. Their common presenting symptoms were dyspnea and cough, and mean duration of illness was 41 days. On chest examination, inspiratory crackle was a common finding. The laboratory findings were nonspecific except hypoxemia. Lung function studies revealed restrictive defect or combined obstructive and restrictive pattern in most patients. Bilateral patchy and nonsegmental alveolar opacities constituted characterized radiographic finding, highlighted on high resolution computed tomogram. It showed a favorable prognosis with an excellent responsiveness to corticosteroid therapy. The clinical features and laboratory findings were similar between domestic and foreign cases except female preponderance in Korean cases. CONCLUSION: If the clinical course is atypical or pregressive under proper treatment, clinicians should reevaluate clinical features and radiographic findings under the consideration of BOOP. Tissue confirmation is recommended for the definitive diagnosis of BOOP.