As shown in Table 1, the total number of children examined was 16,298 in the two cities; 9,828 in Hiroshima (4,716 exposed and 5,112 controls), and 6,470 in Nagasaki (3,606 exposed and 2,864 controls). The number of females predominated over males in both cities as well as in both the exposed and control groups. The exposed group was further divided into three categories by parental exposure status; i.e., children born to parents in which only the father was exposed, only the mother was exposed, or both parents were exposed.

Since efforts were made to collect as many cases as possible in the exposed group, the number of children per parental couple is considerably higher in the exposed group than in the controls (Table 1); 1.4 children per couple (or 8,322 in 5,823) in the exposed, and 1.2 per couple (or 7,976 in 6,473) in the controls, when the two cities were combined.

The mean age of the participants at examination was 24 in Hiroshima, and 23 in Nagasaki with a range between 12 and 38.