29 thyroid owth had developed atrophy of the iated with gland before puberty, and changesassoc assoclpuberty were delayed. There may be some r ation between the apparent increased demandfo ce aran thyroid hormone at puberty and the appe s of thyroid nodules, since in 10 children (4 male and 6 females) thyroid nodules appeared near the expected or actual time of puberty. In 5 other children (2 males and 3 females) the nodules appeared | to 3 years after puberty andin thefemales were associated with pregnancies. In evaluating the influence of puberty and pregnancy it should be pointed out that the latent period between exposure and the developmentof thyroid abnormalities was fairly constant in all these curves Sex Incidence The sex ratio of occurrence of benign thyroid lesions in the Rongelap population was1.3 in females to 1.0 in males. This may be misleading since, in the group exposed at < 10 years of age, all the females had lesions whereas 2 males did not. The fact that all 3 malignantlesions of the thyroid were in females is consistent with reported statistics showing a preponderanceof such lesions in females.26 Discussion By the timethe first malignant thyroid lesion appearedin the more heavily exposed Rongelap group several years ago, numerous benign adenomatous thyroid nodules had appeared. Thelatter were suspected of being related to the radiation exposure, but such an etiological relationship of the single isolated malignant lesion found at that time was speculative. The finding of 2 additional individuals with thyroid carcinoma in this group (3 among 21 thyroid lesions in 67 Rongelap people exposed) makestheetiological role of radiation exposure increasingly probable. For the time being the single malignant thyroid lesion found in a womanfrom Utirik Atoll cannot be attributed to radiation exposure because of the low dose received there. The significance of radiation exposure of the thyroid glandsin the Rongelap people had not thyroid lesions. More careful review of the dose calculations indicated that considerable exposures from radioactive iodine absorption had probably occurred, particularly in the children. The exposure of the Rongelap people was not comparable with exposure of populations due to fallout from reactor accidents in which radionuclides are absorbed chiefly via milk from cattle grazing on contaminatedpastures. The Marshall Islands have no cattle and no local milk supply. (Mother’s milk may have contributed to the radioiodine absorption in 2 children reported to have been nursing at the time of the accident.) But there was heavy contamination of food and water supplies on Rongelap and a relative abundanceof radioiodines in the fallout. The dose to the thyroid glands was greater than that to other organsby a factor of 2 in adults and a factor of about 7 in children. Numerous animal studies have demonstrated the role of radiation in the etiology of thyroid neoplasms.27-29 In humans the developmentof thyroid nodules and cancerfrom x-irradiation,?%41 particularly when the radiation occurs in infancy and childhood,#2-34 is well documented. Development of suchlesions from radioiodines hasalso been seen in animals but less frequently in humans. Sheline et al.39 reported 8 cases of nodular goiter in their follow-up study of 250 cases treated for hyperthyroidism. Six of these cases wereirradiated before 20 years of age and 4 before 10 years of age. One showeda possible invasion of the thyroid capsule. The incidence of thyroid nodularity in the exposed Marshallese is considerably higher than that reported by Pincus?? and Hempelmann*? in their studies of populations who had been exposed to therapeutic x-irradiation of the neck region ata young age. However,on risk per rad basis, the incidence of51 cases per 106 persons per rad-per year for the Marshallese is quite comparable with 24 for one group and 64 for a second group calculated by Pincus and Hempelmann. This companson seems to indicate similar effectiveness — per rad ~ of x-radiation and radioiodine exposure.* The 3 malignantlesions of the thyroid reported here in the heavily exposed Rongelap people appearto be the first such cases clearly associated with radioiodine exposure except for one possibly malignantthyroidlesion reported by Shelineet al.3° *Mr. Keith Thompson of this Laboratory carried out the statistical analyses in the thyroid cases. ‘ : % JOGb28b aaa> correo had posed children, varying between 10 and 13 years, so that the above findings may have been fortuitous. In the 4 women who developed carcinoma of the thyroid the possible influence of the stress of pregnancy must be considered, since all had multiple pregnancies in the years preceding the develop. mentoflesions. been fully appreciated until the appearance of