An epidemiological study is to observe and analyse 100 cases of lung cancer in Korean, which had been diagnosed actually at the general hospitals in Korea from 1970 through 1974, to discover the tendency of the lung cancer by sex, age, occupation, duration of clinical symptoms before diagnosis, site of cancer in lung, size of cancer, occurrence, treatment, prognosis, smoking and pathological findings as follows. 1. Males were affected 5.7 times more than females, the peak incidence of lung cancer were 50 years old age group. 2. The occupations of the cases were commerce, agriculture, industry, laborers and teachers, etc. in thht order. 3. The average duration symptoms from onset to diagnosis were 5.5 months. 4. The cancers were affected more right side than left side of the lungs, Particularly the most of them were affected in the upper lobes of the lungs. 5. The average diameter of the tumors was 5.5crX6.5cm, However the largest of them was 10cm X 13cm. 6. The most cases of the lung cancers were occurred primarily. 7. Out of the 100 cases, 58 cases had no treatment, 23 cases had palliative-symptomatic treatment, of cases by special chemo-therapy, 7 cases by surgery, and 5 cases by cobalt 60 or X-gay. 8. In the view point of prognosis, the most cases of the lung cancers died within one year atfer diagnosis. 9. The smoking was one of the causative factor of lung cancer, but there was no significant diferentiation by means of the amount of smoking. 10. The most cases of the lung cancers diangosed histo-pathologically, were epidermoid(squamous) type.