size exhibited 3 adenomatous nodules, 1 adenoma, 2 carcinomas, and 2 occult papillary carcinomas, one of which may have been a follicular carcinoma. Uncertainty was associated with diagnosis of follicular carcinoma, one in the exposed group and one in the comparison group, because of equally divided opinion among consulting pathologists. However, it was reasoned that both follicular carcinomas could be excluded from a risk coefficient estimate without seriously biasing the results. Diagnoses on five other individuals are pending. All five are from Utirik Atoll; three are in the <lO-year old age group, and two are in the 10= to lL8-year-old age group. METHODS Adams et al. (6) classified thyroid abnormalities following a scheme similar to that used by the World Health Organization and a committee of pathologists who had special expertise in diseases of the thyroid (7). The following nomenclature was used: Adenomatous nodule: a focal proliferative lesion consisting of changes typical of adenomatous goiter; the lesions do not fulfill criteria of true neoplasms. Adenoma: an encapsulated proliferative lesion with a uniform internal growth pattern and benign clinical course. Occult papillary carcinoma: a small nonencapsulated sclerosing carcinoma, considered to be clinically benign even with positive regional Lymph nodes. Papillary carcinoma: larger, infiltrating carcinoma, usually containing both papillary and follicular components. The smallest lesion diagnosed as a papillary carcinoma, by the consultant pathologists, was 0.8 cm in diameter. The recent computation of thyroid absorbed dose was performed for inhabitants of Rongelap, Utirik, and Ailingnae Atolls who were exposed to fallout on March 1, 1954. The amount. of fallout activity taken into the body was estimated from the value of I excreted in urine obtained from 64 persons who were at Rongelap. yee other components of fallout taken into the body, particularly position. I and I, had to be inferred from studies on fallout com- The authors of the reassessment study made dose estimates on the basis of actual BRAVO fallout composition. The intake pathway and the time post-detonation ac which intake was likely to have occurred were obtained from interviews with the exposed people, and historical records and were factored into the new dose estimates. A detailed development of the dose reassessment was reported by Lessard et al. (3). The radioepidemiological tables assembled by the Working Group (8) represented the best scientific judgment for the assignment of cancer risk from external radiation; thus we obtained one estimate of external exposure risk coefficient from this source. For persons less than 20 years of age, the Working Group adopted an average risk coefficient of 3.3 excess cancers per milifon person-rad-years at risk, and for persons 20 years or older they chose a value of 1.0 excess cancer per million person-rad-years at risk. minimum latent period was chosen for thyroid cancer. A 10-year The Working Group calculated thyroid cancer risk based on a linear dose-response function and maintained that the estimates of risk applied to external x and gamma irradiation, but not to the intake of radioisotopes of iodine. The BEIR III (1) risk coefficients were based, in large part, on external 21