Eleven patients with proved Bronchiolo-aveolar cell carcinoma were found in th echest department of the national menical center from 1975 to 1981. The incidence of Bronchiolo-alveolar cell carcinoma is recently increased as primary lung carcinoma. The result as follow. 1. The ratio of male and female was 5 : 6, and an incidence of 4.4% among total primary lung cancer patients. The highest incidence (3 of cases) was seen in the sixth decade, and the remaining cases were evenly distributed in the third, fourth, and fifth decades of life. Among them youngest was 29 years old and the oldest was 66 years old. 2. Clinical and radiological initial diagnosis prior to the final diagnosis were as follows ; pulmonary tuberculosis ; 7 cases, pneumonia ; 1 case, bronchiectasis ; 1 case, and lung cancer ; 2 cases. 3. Radiological examination of chest presented several pictures ; most commonly, homogenous or patchy infiltrations ; 6 cases, nodular or mass like densities ; 2 cases, disseminated nodular or military patterns ; 2 cases, and reticular pattern ; 1 case. 4. Bronchogram reveald no contributable findings except one case of complete tappering obstruction of the segmental bronchus. Therefore we arrive at the conclusion that early diagnosis will result in increased resectability and improved survival so aggressive diagnositic work-up for suspicious pulmonary infiltrate is necessary.