Cancer (with the exception of leukemia) which had often been observed among atom bomb survivors was discussed. Prevalence of thyroid carcinoma was high in the people who had been exposed to more than 50 rad of the atomic radiation. A great difference in prevalence of cancer was seen between irradiated people whose age had been under 20 years at the time of exposure and non-irradiated. More women than men had papillary adenocarcinoma. The highest prevalence was seen 16 to 20 years after exposure to atomic radiation, but there was no difference in prevalence between those from Hiroshima and from Nagasaki. Lung cancer comprised 89% of all cancers of the people whose age was 50 years and over. Most of them had been exposed to atomic radiation of more than 300 rad. The type was cellular retrograde cancer. The prevalence of gastric carcinoma was low, and breast cancer occurred at an early age before menopause. The occurrence of cancer in juvenile survivors was several times higher in the patients who had been exposed to atomic radiation of more than 100 rad than in non-irradiated. These values indicate that cancer occurs more frequently than leukemia does in such survivors.