In response to the recommendations of the 1955 Francis Committee, the Atomic Bomb Casualty Commission (ABCC) used data from the A-bomb survivors survey, conducted at the time of the 1950 Japanese national census, to develop a comprehensive roster of persons eligible for inclusion in fixed study cohorts. The survey identified 284,000 Japanese survivors, of whom nearly 200,000 were resident in either city at the time of the census. Subsamples of this original Master Sample have formed the basis for all studies conducted by ABCC-RERF since the late 1950s (Table). In all mortality studies, information on cause of death, regardless of location in Japan, is obtained through official permission from the Ministry of Health, Labour and Welfare and the Ministry of Justice. Information on cancer incidence is obtained through the local tumor and tissue registries and is limited to current residents of Hiroshima and Nagasaki prefectures. Additional information on disease incidence and health status is available for the Adult Health Study (AHS) participants.