[en] We previously reported that there was a high correlation between the exposure dose and the incidence of skin cancer in A-bomb survivors using the data of the Nagasaki Life Span Study of Radiation Effects Research Foundation and Nagasaki Tumor Registry. In Report 3 of this series, we clarified that the correlation between the exposure distance and the incidence of skin cancer was statistically significant in 140 cases of skin cancer collected from 31 hospitals in Nagasaki City and adjacent districts on the basis of the data of the total 66,276 A-bomb survivors recorded in the Scientific Data Center of Atomic Bomb Disaster, Nagasaki University School of Medicine, and that the correlation was the same even when the cases were divided by sex. In this report, we examined the chronological change of the incidence of skin cancer in Nagasaki A-bomb survivors, using the data of the Scientific Data Center of Atomic Bomb Disaster. It is likely that the incidence of skin cancer in Nagasaki A-bomb survivors has increased after 1962, especially after 1975 in those exposed within 2.5km from the hypocenter compared to those exposed at 3.0km or more. (author)