ence of antithyroglobulin antibodies in unexposed versus exposed groups (Morimotoet al., 1987). In addition, no difference in the prevalence of chronic thyroiditis was found in children considered exposed or unexposed to radioactive fallout in Utah and Nevada (Rallison et al., 1974). Notably, in that study the prevalence of elevated titers of antithyroglobulin antibodies in children with “normal” thyroids was 4.8%. Hypothyroidism is common in aging populations, and in the Framingham Heart Study a clearly elevated thyrotropin (TSH) level was foundin 4.4% of persons older than 60 years (Sawin et al,, 1985a). The prevalence of antimicrosomalantibodies also increases with age: two-thirds of elderly persons with evidence of thyroid hypofunction had significantlevels of antimicrosomal antibodies (Sawin et al., 1985b). The Marshallese data suggest that autoimmune thyroid disease is not common in that population, regardless of a history of radiation exposure. tality from radiation exposure is low when comparedto naturally occurring cancer mortal- | ity it is not surprising that there is no observed increase in mortality among the radiationexposed Marshallese. Nevertheless, much at- — tention has been addressed to their cancerrisk. On the other hand, limited attention has been given to morbidity from nonmalignant disease, principally of the thyroid, as a late consequence of radiation exposure, and yet these lesions have been ofgreat clinical importance (Table 5). A. Thyroid surgery: Twenty-six (30 %) of the Rongelap group and eighteen (11%) of the Utirik group have had surgeryfor thyroid nodules that were ultimately found to be benign. The types of thyroid nodules found in the exposed population since 1963 can be grouped into cancers, adenomas, and adenomatous nodules. Cancers and adenomas are neoplasms. Adenomatous nodules, which, like adenomas, are benign, are not properly catego- rized as neoplasms, Histologically, they are hyperplastic lesions. In the exposed population both benign nodules and thyroid hypofunction display a similar correlation with radiation dose (Fig. 5), and, in contrast to thyroid cancer, adenomatous nodules have been very common(see Table 3). Adenomatous nodules are rarely of clinical significance, because they do not evolve into carcinoma. Surgery is necessary only to NONCANCEROUS THYROID MORBIDITY IN EXPOSED MARSHALLESE The late somatic effects of exposure to ionizing radiation have been equated with cancer induction, the ultimate measureof thoseeffects being expressed in mortality. Since cancer mor- TABLE 5: LATE THYROID MORBIDITY UNRELATED TO DIAGNOSIS AND TREATMENT OF THYROID CANCER IN 253 RADIATION-EXPOSED MARSHALLESE. Morbid event Number of cases Thyroid surgery for benign lesions 44 Hypothyroidism, radiogenic 15 Hypothyroidism, postsurgical 21 Hypoparathyroidism, postsurgical Recurrent laryngeal nerve palsy Pituitary tumor’ Total morbid events * Possible association (Adams et al., 1984). 14