BACKGROUND: Mixed obstructive and restrictive pattern of spirometry can not be concluded in the presence of true restrictive disorders because pure obstructive disorders can also shoy reduced vital ca pacity. However, it is not known how many patients with mixed spirometric pattern really have restrictive disorders in Korea whose pattern of pulmonary diseases is somewhat different from foreign countries. To answer this question, I performed this study and tried to answer it according to diseases in addtion. METHOD: Test results from 413 patients who undergone both spirometry and lung volume measurements on the same visit from August 1, 1998 to July 31, 1999 were included. Spirometry data were classified as mixed obstructive-restrictive pattern when spirometry showed 'FEV1/FNC <70% (<65% if age >or= 60)' and FVC <80% of predicted value. TLC by the method of nitrogen washout was considered as gold standard to diagnose restrictive disorders in which TLC is less than 80% of predicted value. RESULTS: Out of 404 patients who could be evaluated, 58 had mixed pattern of spirometry. 58 patients were suffered from airway diseases (39 patients) such as COPD (22 patients, 38%), asthma (11,19%), bronchiectasis (6,10%), and sequelae of pulmonary tuberculosis (15,26%) or other diseases (4,7%). Only 18 out of 58 (31%) were confirmed to have true restrictive disorders by TLC. The proportion of true restrictive disorders was different according to diseases, 20.5%(8/39 patients) in patients with airway diseases and 53.5%(8/15) with sequelae of pulmonary tuberculosis (p<0.05). CONCLUSION: Many patients whose spirometry showed mixed pattern didn't have restrictive disoders but had pure obstructive disorders. This was true for more patients with airway diseases. Therefore it would be prudent that lung volume be tested to diagnose restrictive disorders in patients with mixed spirometric pattern.