Plain chest films are the most useful modality in diagnosis of primary lung cancer, but it is difficult to interpret the radiologic findings by histological types. Authors reviewed chest films of 324 cases of histologically confirmed primary lung cancer from January 1974 to April 1982 at Seoul National University. The results are as follows : 1. Incidence was most common in the 6th decade as 34.4%. Male to female sex ratio was 3.8 : 1 and there was no sex difference in Adenocarcinoma. 2. Distribution of histologic types of primary lung cancer as follows ; squamous cell Carcinoma 50.6%, Small Cell Carcinoma 22.5% lange Cell Carcinoma 9.3% Bronchegenic adeno caranoma 10.5% Bronchioloalveolar Cell Carcinoma 1.9%, Adenosquamous Carcinoma 0.6%, Carcinoid Tumor 0.3%, Adenoid Cystic Carcinoma 0.3%. 3. Radiologic findings by histologic types are as follows : a) Squamous cell carcinoma commonly present as collapse (51.8%) peripheral mass (40.8%), pneumonitis (37.2%), hilar involvement (34.8%), and in single abnormality, peripheral mass (44.8%). b) Small cell carcinoma commonly present as hilar involvement (78.1%), mediastinal widening or mass (53.4%) and in single abnormality, hilar involvement (58.3%). c) Large cell carcinoma commonly present as hilar involvement (50%) pneumonia (46.7%), collapse (40%), peripheral mass (36.7%) and in single abnormality, large peripheral mass (33.3%). d) Bronchogenic Adenocarcinoma commonly present as peripheral mass (44.1%), collapse (41.2%), pleural effusion (35.2%) and in single abnormality, peripheral mass (50%). e) Solitary peripheral mass commonly present as lobulation (48%) and spiculated margin (51%), but no specific findings by histologic types. Cavitary formation was most common in Squamous cell carcinoma.