There are many pathogenetic factors for collapse of right middle lobe; profuse peribronchial clustering oflymphnodes about the right middle lobe bronchus, poor drainage of the bronchus because of its acute angle oftake-off from the intermediate bronchus, and the isolation of this small lobe from the right upper and lowerlobes, and thus from the aerating effects of collateral ventilation. Retrospectively we reviewed 36 cases of rightof right middle lobe collapse of which causes were confirmed by histopathologic or bronchogaphic findings duringthe recent 6 years from March 1983 to february 1988 at Inje college Pusan Paik Hospital, and obtained thefollowing results: 1. Male to female ratio was1:1.4, and peak incidence (64%) was in the fifth and sixth decadeswith the mean age of 51.1 years. 2. Bronchiectasis was the most common cause (30.6%), and the others were chronicbronchitis (25.0%), pulmonary tuberculosis(19.4%), lung cancer (16.7%), and non-specific inflammatorydisease(8.3%). this suggests benign disease is 5 times more common cause of right middle lobe collapse than lungcancer. 3. Among the plain chest radiolograph findings, obliteration of right cardiac border and triangularradiopaque density were the most frequent findings(77.8% in each) and the next was downward and anteriordisplacement of minor and major fissures(55.6%) 4. Bronchography was done in 11 cases: bronchiectasis was found in8 cases and chronic bronchitis in 3 cases. Right middle lobe bronchus was obstructed in 2 cases of chronicbronchitis. 5. Chest CT scan was performed in 4 cases of lung cancer, 2 of non-specific inflammatory disease, and1 of pulmonary tuberculosis: all of lung cancer revealed hilar mass, buldged or lobulated fissures, inhomogenousdensity, and mediastinal lymphnode enlargement, and all benign diseases showed homogenous density and flat toconcave fissures. right middle lobar bronchus narrowing was seen in 5 cases and its obstruction in 2 cases.