W. H. ADAMS: LATE MEDICAL CONSEQUENCESOF EXPOSURE TO RADIOACTIVE Hypothyroidism, Postsurgical Despite efforts to mitigate loss of thyroid tissue, however, there continues to be evidence of an inordinantly high frequency of postsurgical thyroid hypofunction among the exposed population. Table 9 showsdata obtained through 1987 illustrating this point. An increase in frequency of Table 9 Marshallese with previously normal TSH levels who have developed elevated levels following thyroid surgery Exposure Adult Number Number group thyroid with with Percent dose (rad)* surgery hypothyroidism** Rongelap*** 1200 23 14 61 Utirik 160 25 7 28 Comparison None 11 1 8 * Average estimated dose for an adult male ** Biochemical evidence of thyroid hypofunction as indicated by at least two determinations of thyroid stimulating hormone > 7.0 uU/1. Normalvaluesare less than 6.0 uU/1. *** Routine thyroxin suppression prescribed. postsurgical thyroid hypofunction with increase in thyroid radiation dose is apparent, even though all thyroid surgery patients were advised to take thyroxin. However, the data in Table 9 must represent a minimum estimate of the prevalence of postsurgical thyroid hypofunction, for thyroxin was not purposely discontinued before testing. Some persons may have maintained normal serum levels of thyroid hormoneafter surgery only because they are adhering satisfactorily to the prescribed thyroxin regimen. In conclusion, these data reveal an inordinantly high frequency of postsurgical thyroid hypofunction in exposed persons whohad normalthyroid function prior to surgery. Therefore, there appears to be significantly diminished thyroid reserve in many exposed persons, and althoughthis diminution is not apparent from routine testing of hormone levels, it frequently can be clinically unmasked by thyroid surgery. M3 288