The mass survey was carried out for the purpose of early lung cancer detection by annual chest roentogenography in Okayama Prefecture. For 9 years from 1973 to 1981, the total number of those examined was 2,014,098; seventy percent of them were aged 40 and older. Four hundred twenty-eight cases of lung cancer (237 males and 191 females) were detected in this survey. The incidence was 21.25 per 100,000 and 52.71 per 100,000 in males aged 40 and older. More than half of them were older than 70 years old. 82.5 percent of lung cancer detected in this survey was peripheral type lung cancer. Most frequently the diameter of the tumor shadow was small; 32.5% was less than 2cm and 29.1% from 2 to 3cm. Histologically, the lung cancer detected in this survey was diagnosed, 53% as adenocarcinoma, 31.4% as squamous cell carcinoma, 8.7% as small cell carcinoma, and 2.9% as large cell carcinoma. Most of the lung cancer detected in this survey was in the early stage; 79.3% was in stage I and Ⅱ. Surgical resections were carried out on 61% of them. The mass survey was very effective in detecting early peripheral type lung cancer. But it was not effective in detecting early hilar type. Cytological examination of sputum should be performed on smokers aged 40 and older to detect early hilar type lung cancer.