One-hundred-twelve patients with pulmonary adenocarcinoma 2cm or less in diameter on chest rediograph were found by mass screening between 1981 and 1989. Of these patients, 92 underwent surgical resection of the tumor. To detect early pulmonary adenocarcinoma more efficiently by mass screening using annual chest rediographs, clinical and radiographic features of the 92 patients were examined and the following results were obtained. 1) Twenty-nin patients with a tumor 1.5cm or less in diameter on the resected specimen were all in pathological atage I and the five-year survial rate was 100%. 2) In 63 patients with a tumor between 1.6cm and 2.0cm in diameter, the five-year survival rate was 83.5%. Of those, 6(13%) patients had advanced lung cancer, all of which could be detected on the previous chest radiograph by retrospective analysis. These results indicate that efforts to detect tumors 1.5cm or less in diametor are important to improving the efficiency of mass screening. For this purpose, it is necessary to obtain a chest radiograph of good quality and learn to identify the radiographic features of early pulmonary adenocarcinoma.