25 year-old female (3¢18) who was 21 years of age at exposure and a 21-year-old female (472) who was 6 years of age at exposure. This latter case presented the first malignant thyroid lesion noted in the group of heavily exposed children, who have the highest incidence of benign lesions. These recent findings greatly increase the concern about radiation-induced neoplasmsin this population. Thethird malignant lesion was in a woman from Utirik Island. Since the dose of radiation received by that group wasvery low,it is highly improbable that this lesion is attributable to radiation exposure. Surgical Exploration of Thyroid Nodules Thyroid operations have been preformedat the following times: 3 in 1964,* 3 in 1965,** 5 in 1966,** 4 in 1968,** and 5 in 1969.t¢ (Hospital summaries of cases operated in 1968 and 1969 are presented in Appendix 5.) At surgery the gross appearance of mostof the thyroids was lobulated, but in addition they contained grossly discrete masses (see Figures 22 to 24). The benign thyroid lesions exhibited multiple nodules varying in size from a few millimeters to several centimeters in diameter. They varied from soft to firm in consistency, and were hemorrhagic or in many Instances cystic. Some thyroid glands _ had increased fine vascularity over the surface similar to that noted in thyroids previously trdated with large doses of 1311 for hyperthyroidism. Some of the recent patients were given small tracer doses of radioiodine the day before surgery so that the radioactive content of the nodular tissue could be measured at the time of surgery. The discrete lesions in many cases showed 131] uptake different from that of the extra-nodular tissue, most discrete benign lesions showing less uptake (Figure 25). Radioiodine in malignant tissue was found to be nil compared with that in surrounding normal tissue. Microscopic examination of the benignlesions revealed marked variationin size offollicles. The cells of some follicles appeared atrophic, while others were hyperplastic, which was reminiscent of iodine deficiency goiter (Figure 26). In addition to the gross adenomatous masses, someof the 15 thyroids classified as benign contained multiple “By Captain C.A, Broadus (MC)USN,U.S. Naval Hospital, Guam. **By Dr. B.P. Colcock, New England Deaconess and Bapist Hospitals, Boston, Massachusetts. tBy Dr. B.M. Dobyns, Cleveiand Metropolitan General Hospital, Cleveland, Ohio. microscopicclusters ofwhat appearedto be atvpical proliferating ceils here and there in the parenchyma(see Figures 27 and 28). From the microscopic examination the thyroid carcinomas were considered of low grade malignancy, andthey varied in structure from papillary to mixed papillary andfollicular type (Figures 29 and 30). Benign adenomatous changes werealso noted in the glands. All showed capsular invasion. and in two cases localized metastases to lymph nodes were present and in twoother cases, blood vessel metastases. Total thyroidectomies were performed in all three cases of malignancy, and left radical cervical lymph nodedissection also was done in one case because ofspread to lymph nodes. No metastases have been recognized beyond the cervical region in any patients. Thyroid Function: Correlation With Retardation of Growth in Children In somechildren with thyroid lesions, deficiency in serum thyroxine has been correlated with re- tardation of growth. The moststriking instances of hypothyroidism were in two boys who showed marked retardation of statural growth and bone age. By 1964, they had developed obvious atrophy of the thyroid gland with almost complete loss ot thyroid function as evidenced by failure of the thyroid to take up much if any lodine even alter TSH stimulation. By this tume their blood had low thyroxine and very high TSH levels. They showed bony dysgenesis, sluggish Archilles tendon reflexes, puffy faces, and dry skin. Their response to thyroid hormone supplement as evidenced by growth spurt, improved appearance, etc., has been dramatic (see Figures 31 to 33). Several other children whodisplayed thyroid nodularity and whose statural growth was below average showed lowor low-normal serum thyroxine values and poor radioiodine uptake after TSH stimulation indicating that their thyroids were functionally impaired and operating near their maximum capacity. Functional deficiency of the thyroid was not demonstrated in aduits with nodules or carcinoma of the thyroid. Influence of Physiological Stress on Thyroid Abnormalities An assessment was madeof therelationship of the development of puberty to the occurrence of thyroid nodules. Degrees of pubescent changes have been recorded annually by a grading system. The two boys who showed greatest retardation of