Retro-illumination photography was utilized for epidemiological studies of cataract. Diagnosis of cataract was made by the existence of shadows on the photographs obtained. In the prevalence study, prevalence rate of cataract was 35.7% in all (30.2% in male and 45.1% female) 1,017 persons (643 males and 347 females). Prevalence rates were always higher in females than in males, and in diabetics as compared with non-diabetics, in all decades of life. The progression study in 338 persons (144 males and 194 females) revealed that maturing courses of cataract were most rapid in diabetic females in the fifth to seventh decades of life.