INTRODUCTION: Thefollow-up of populations exposed to ionizing radiation may be warranted on humanitarian and scientific grounds. On March 1, 1954, the residents of several islands in the Marshall Islands’ chain were exposed accidentally to fall-out from a planned test ofa nuclear device at the Bikini Atoll Test Site. The populations of three islands were identified for prompt and extended medical evaluation, and treatment of any acute wholebody andlocaleffects resulting from this exposure. Subsequently, a congressionally mandated follow-up program was implemented by the U.S. Atomic Energy Commission (AEC). By this program, the populations of the three affected islands and a comparison group selected from amongthe islands considered to have been unexposed, were to be surveyed at regular intervals to monitor the health of these populations, and thereby to identify and evaluate adverse long-term health effects with respect to exposures to radiation in 1954. The general medical care of the Marshallese populations was the responsibility of the governmentof the Trust Territory in whose jurisdiction the Marshall Islands resided. This program has continued to the present with some interim modifications in its scope and objectives. These changes reflected redefinition of the exposed populations, and temporal changes in general health care delivery, and in the sociopolitical and cultural environments. of the islands (1). In addition to the benefits of routine medical monitoring to the longterm health of the Marshallese, a major outcome of the program has beenits contributions to scientific knowledge about the health effects of radiation generally and specifically about the risks of exposure of the thyroid gland to short-lived isotopes of iodine (2). The results of the immediate medical response to the accident in 1954, and of the subsequent periodic medical surveys conducted through 1989 have been reported in a series of technical reports (3-19) and in referred scientific journals (20-24). In addition, an extensive bibliography has been compiled of reports, journal articles, book chapters and other publications that concern the radiological and other technical aspects of the event and its sequelae, as well as related general and specific biological and medical topics (25). With the transition from a trust territory government to the Republic of the Marshall Islands, this program has continued under the new government with Brookhaven National 1