Two cases of typical cataract caused by atomic bomb radiation were observed. Both patients were male and had been exposed near the hypocenter (950m and 140m from the hypocenter) when they were young (12 years and 5 months, and 15 years and 3 months). Wounds at the exposure were not fatal, but their exposure doses were close to the lethal dose (570 and 609 rad). Their acute symptoms were severe. Nevertheless, their symptoms recovered by rest and good nutrition. Lenticular opacities (delayed ocular damage caused by atomic radiation) occurred in one patient 3 years and 7 months after the exposure and in the other patient 4 years after the exposure. It was 33 years and 10 month after the exposure when both patients aged 45 and 48 had senile cataract. Effects of aging on both patients exposed to large doses of radiation in young ages were suggested.