Nefzger, M. D. (Follow-up Agency, National Research Council, 2101 Constitution Ave., Wash., D. C. 20418). Follow-up studies of World War II and Korean War prisoners: 1. Study plan and mortality findings. Amer. J. Epid., 1970, 97: 123–138.—U. S. Army men taken captive during World War II and the war in Korea, and various other groups, were followed for mortality to 1965. Standard mortality ratios and death rates indicate a clear early excess of deaths among prisoners held by the Japanese in World War II. Relative to their controls, excess mortality in Pacific prisoners diminished with time, the two groups being indistinguishable by the mid-1950's. Prisoners from the European and Mediterranean areas of World War II have not had an adverse mortality experience to 1965. Mortality in Korean War prisoners has been more like that in Pacific than European prisoners! A substantial early excess of deaths has, relative to partially matched controls, all but disappeared. Korean War prisoners remained at about the same disadvantage throughout 12 years of follow-up in relation to mortality in U. S. white males, whereas Pacific prisoners did not. Accidents, tuberculosis, and cirrhosis of the liver appear to be the causes chiefly responsible for the excess deaths in Pacific prisoners. Trauma is the most common cause of death, and of excess death, in the younger Korean prisoners.