Somewhatlater, an additional 200 persons thought at the time to be unexposed, and who had moved to Rongelap from neighboring atolls, were added to the group and followed medically at yearly intervals. Over the years the composition of the control group has varied due to non-participation, mortality, and loss to follow-up. As of the 1989survey, approximately 135 persons were still participating, including 60 remaining from the original unexposed group of 86. Follow-up by BNL at that time identified 26 of the original unexposed group as deceased. 5.1.2 Findings The medical findings of the visiting teams have been described in the literature. The early effects are described in Section 4.5. The most frequently observed late effects in the exposed Marshallese were thyroid abnormalities. Growth retardation though to be related to hypothyroidism was observed andits relationship with radiation was established. Benign and malignant thyroid nodules developed beginning nine years following the event. One case of acute myelogenous leukemia, probably related to radiation exposure, was diagnosed in 1972. In addition, the general health of the. population has been documented. Other malignancies have been seen and therapy provided. The relationship of these latter malignancies to the exposure is not known and cannotbe firmly established due to the conditions discussed in Section 5.5. Without individual thyroid dose estimates, radiation exposure cannotbe established to be causal. However, other risk factors (dietary iodine deficiency, head. and neck irradiation for medical purposes, dietary or environmental goitrogens) did not appear to be prominentin this population. 5.2 What Shouid Have Been Done The medical surveillance of the Marshall Islanders from 1954 through 1992 cannot be faulted considering the geographic, transportation, social and political considerations of the area, and due to the lack of dose information on specific individuals. These services included detailed medical examinations that comprise all feasible medical history, clinical examinations, Norton. and hematological testing, that were possible under the field 30