Figures 1 and 2 show the age distribution of thyroid nodules in the various populations. The greater prevalence of nodules in the younger age group of exposed Rongelap-Ailingnae people is in contrast to the greater prevalence in the older age groups in the comparison population. The latter distribution has been noted in other unexposed world populations (see Table 4, Appendix I). Figure 3 shows the cumulative percentage of thyroid nodules for the different age and exposure groups over the years. The curve of cumulative in- crease appears to be leveling off for the Rongelap and Ailingnae groups over the past decade, as would be expected, since the numbers of unaffected people are fewer. The Utirik group shows a slight increase. Sex ratios of thyroid nodules (surgical cases only) were as follows: Group Exposed Unexposed* Total nodules Benign M/F Carcinomas M/F 10/35 10/28 6/14 2/13 M/F 0/7 4/i As has been noted in other populations of the world, the preponderance of thyroid nodules was in the females in both exposed and unexposed populations. In the Marshallese, though the males accounted for a larger fraction of nodules in the exposed than in the unexposed groups, the reverse was observed for cancer. The number of cases is too small for this finding to be meaningful. The ratic of benign to malignant lesions for the exposed groups was 38/7 and for the unexposed 15/5. As pointed out in previous reports, the radiation exposure may have reduced the cancer ratio in the exposed group (“overkill" effect) compared with that in the unexposed group. (ec) Gross Findings at Surgery Because of the care taken in clinical examinations, thyroid nodules were often detected and surgically explored while still quite small. Though many of these were thought to be single nodules by palpation, most were found at surgery to be multiple. Thyroid glands were seldom diffusely enlarged. Aside from the nodules that were present, the remainder of the glandular parenchyma consistently appeared normal on gross examination. When pathologically malignant lesions were discovered, they were often not the nodules that had drawn primary attention preoperatively. In addition to distinct nodules, any areas with gross irregularities were also resected, no matter how minute. It is noteworthy that some thyroids, particularly in earlier cases among the exposed Rongelap group, showed increased numbers of fine tortuous capil~ laries over the gland surfaces. These resembled thyroids seen in certain cases of Grave's disease that had been inadequately treated with 13ly and were eubsequently treated by thyroidectomy. This feature has not been noted in the irtadiated people from Utirik. *The Likiep and Wot je groups were not included since they were seen only once. - 61-