The incidence rate of "active" pulmonary tuberculosis (TB) cases with bacteriological confirmation or cavitary lesions on chest radiographs was studied among population screened with mass miniature radiography in Funai-Gun, Kyoto Prefecture from 1982 to 1993. The results were as follows: Among population of 40 and over, prevalence rate of all fibrotic lesions on chest radiographs among male (8.3%) was twice as high as that of female (3.8%). The rate of moderate or extensive fibrotic lesions among male (3.3%) was three times as high as that of female (1%). The higher the age of the population, the higher the prevalence rate of radiological fibrotic lesions both in male and female. In male, in particular, prevalence rate of moderate or extensive fibrotic lesions started to rise after 40 years of age, became much higher after 70 years of age and reached 8.1% after 80 years of age. In female, however, it started to rise at 50s (0.3%) gradually and reached only 2.3% after 80 years of age. The incidence rate of "active" pulmonary TB among male of 40 years and over with moderate or extensive fibrotic lesions (4.2 per 1000 person-years) was 16 times as high as male of 40 years and over with normal chest X-ray finding (0.26 per 1000 person-years). Similarly, the incidence rate of "active" pulmonary TB in female of 40 years and over with moderate or extensive fibrotic lesions was 24 times as high as among female with normal finding, and the difference was statistically significant (p < 0.001). From the data obtained and bibliographical review, benefits of INH prophylaxis were discussed.