Clinicians, by their patterns of referral to colleagues in nuclear medicine or surgery, may strongly influence the selection of 131I versus surgical treatment for patients with toxic thyroid adenoma. The information presented here is intended to aid them in making an informed choice. As nodule size of an adenoma increases from 2 cm to 6 cm, the amount of radioiodine administered to the patient to deliver the same dose (30 000 rads to the nodule center, assuming a 30% uptake) increases from 5.6 mCi to 135 mCi. Concurrently, the suppressed thyroid tissue receives a radiation dose as high as 2300 rads. Despite these potentially carcinogenic doses, few patients with radioiodine-induced thyroid tumors have been reported; we discuss possible reasons for this. For young patients with large nodules, surgery is preferred.