It is well known that primary lung cancer is one of the most common malignancies in Korea. With respect to thehistologic type, primary lung carcinoma manifests itself in a number of different ways. The authors analyzed theCT findings of 183 cases of pathologically confirmed primary lung cancer form 1983 to Aug. 1987 without priorinformation of histologic types. The results are as follows. 1. The distributionof histologic types of primarylung cancer was as follows: epidermoid carcinoma, 96 cases (52.5%); adenocarcinoma, 43 cases (23.5%);undifferentiated large cell carcinoma, 17 cases (9.2%) and undifferentiated small cell carcinoma, 27 cases(14.8%). 2. The male to female ratio was 3.9:1, the highest ratio occuring in undifferentiated small cellcarcinoma 12.5:1 and the lowest ratio in adenocarcinoma 1.1:1 where there was no significant difference in themale to female ratio. 3. Chest CT findings by histologic type were as follows: (a) Epidermoid carcinoma(96 cases): The central type was the most prevalent (52 cases )with an incidence of 54%. Major air way obstruction was mostfrequently encountered in this type and was complete in 60% of the cases and partial in 25%. (b) Adenocarcinoma(43 cases ): The peripheral type was the most prevalent (28 cases) with an indicence of 63%. Lung to lungmetastasis was 23%, more common than other histologic types. (c) Undifferentiated large cell carcinoma(17 cases):The highest incidence occurred in the peripheral type, 9 cases (53%). Chest wall involvement was 12%, more commonthan other histologic types. (d) Undefferentiated small cell carcinoma(27 cases ): 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 otherhistologic types. In summary, primary lung cancer showed some difference in growth and propagation on chest CTaccoridng to histologica types.