OBJECTIVE:When using radioiodine for hyperthyroidism there is no consensus regarding the administration of fixed or calculated doses. Guidelines do not specify the preferable approach or the parameters to use to calculate the dose. Therefore, the dose might be quite different with regard to the chosen procedure. This study was undertaken to evaluate the variability of the amount of radioiodine administered in Belgium in various cases of hyperthyroidism. DESIGN AND PATIENTS:Twenty-one Belgian nuclear medicine physicians received summarized clinical files from 10 patients suffering from overt hyperthyroidism (n = 7) or subclinical hyperthyroidism (n = 3). Five patients had homogeneous goiters, one had multinodular goiter, and four had hot nodule. Participants had to determine the radioiodine dose (millicuries, mCi) they would give in each case. RESULTS:Proposed doses varied between 2 mCi and 25 mCi. Mean proposed dose for nodular disease was 10.71 mCi; it was 6.79 mCi for homogeneous goiter. For individual cases, a difference between the lowest and the highest dose of more than 17 mCi was observed in more than 50% of the cases. CONCLUSIONS:We believe that more precise guidelines are mandatory, underlying uncertainties, controversies but recommending however, as minimal and maximal doses to administer, as well as clinical and biological parameters, if any, to be taken into account in order to modulate these doses.