There are many pathogenetic factors for collapse of right middle lobe; profuse peribronchial clustering of lymphnodes about the right middle lobe bronchus poor drainage of the bronchus because of its acute angle of take-off from the intermediate bronchus and the isolation of this small lobe from the right upper and lower lobes and thus from the aerating effects of collateral ventilation. Retrospectively we reviewed 36 cases of right of right middle lobe collapse of which causes were confirmed by histopatholofic or bronchographic findings during the recent 6 years from March 1983 to February 1988 at Inje College pusan Paik Hospital and obtained the following results: 1. Male to female ratio was 1:1.4 and peak incidence (64%) was in the fifth and sixth decades with the mean age of 5.11 years. 2. Bonchictasis was the most common cause (30.6%) and the others were chronic bronchitis (25.0%) pulmonary tuberculosis (19,4%) lung cancer (16.7%) and non-specific inflamma-tory disease(8.3%) This suggests benign disease in 5 times more common cause of ritht middle lobe collapse than lung cancer. 3. among the palain chest radiolograph findings obliterationof right cardiac border and was downard and anterior displacement of minor and major fissures(55.6%) 4. Bronchography was done in 11 cases : bronchiectasis was found in 8 cases and chronic bronchitis in 3 cases. Right middle lobe bronchus was obstructed 2 cases of chronic bronchitis. 5. Chest C-T scan was performed in 4 cases of lung cancer 2 of non-specific inflammatory disease and 1 of pulmonary tuberculosis: all of lung cancer revealed hilar mass buldged or lobulated fissures inhomogenous density and mediastinal lymphnode enlargement and all benign diseases showed homogenous density and flat to concave fissures. Right middle lobar bronchus narrowing was seen in 5 cases and its obstruction in 2 cases