The events prior to Bravo Shot-Operation Castle that led to a decision not to evacuate the Marshallese prior to testing the thermonuclear bombs are presented as are the actions taken after the fallout incident in evacuating the exposed Marshallese and the military personnel. The initial medical effects (findings during first 6 wk after exposure) are briefly described and are followed by description of long term effects, namely, induction of one case of fatal acute myeloid leukemia and a large number of thyroid tumors (benign and malignant) in addition to hypothyroidism in adults and children and two cases of cretinism. The hypothyroidism and cretinism responded well to administration of oral thyroxine. During the first 25 y, there was also much unrest and political agitation initiated by exposed and unexposed Marshallese who were very unhappy as a result of relocation and inability to return to their homelands and feeling that all illness and deaths were due to the mysterious radiation, which they understandably did not understand. The difficulties in part were ameliorated by financial aid from the U.S. Congress. In view of one of us (EPC), no one agency or person in the U.S. Government was willing to take the responsibility for care of the Marshallese and its financing. The exposed and nonexposed Marshallese had their lifestyle changed, some of their homelands made uninhabitable for several years and could aptly be called "nuclear nomads," an expression coined by others.