It is well known that primary lung cancer is one of the most common malignancies in Korea, With respect to the histologic type primary lung carcinoma manifests itself in a number of different ways. The authors analyzed the computed tomographic (C-T) findings of 183 cases of pathologically confirmed primary lung cancer from 1983 to Aug, . 1987 without prior information of histologic types. The results are as follows. 1. The distribution of histologic types of primary lung cancer was as follows : epidermoid carcinoma 96 cases (52.5%) adenocarcinoma 43 cases (23.5%) undifferentiated large cell carcinoma 17 cases (9, 2%) and undif-ferentiated small cell carcinoma 27 cases (14.8%) 2. The male to female ratio was 3.9:1 the highest ratio occuring in undifferentiated small cell carcinoma 12.5:1 and the lowest ratio in adenocarcinoma 1.1:1 where there was no significant difference in the male to female ratio. 3. Chest computed tomographic findings by histologic type were as follows : (a) Epidermoid carcinoma (96 cases) : The central type was the most prevalent (52cases) with an incidence of 54% major air way obstruction was most frequently encountered in this type and was complete in 60% of the cases and partial in 25% The incidence of cavitating malignancy was 10% more common than other histologica types. (b) Adenocarcinoma (43cases): The peripheral type was the most prevalent(28 cases) with an incidence of 63% Lung to lung metastasis was 23% more common than other histologic types. (c) Undifferentiated large cell carcinoma (17cases) : The highest incidence occurred in the peripheral type 9 cases (53%). Chest wall involvement was 12% more common than other histologic types. (d) Undifferentiated small cell carcinoma (27cases) : the central type (19 cases) presented the highest incidence(70%) Major air way obstruction was noted less severe than epidermoid carcinoma : complete 33% partial 63%. the incidence of pericardial effusion and/or thickening was 18% more common than other histologic types. In summary primary lung cancer showed some difference in growth and propagation on chest computed tomography according to histologic types.