Preoperative excess iodide administration for patients with Graves’ disease has been widely adopted by surgeons to perform surgery safely, because it decreases blood flow in the thyroid. However, surgeons often encounter the enlargement of thyroid volume after iodide administration, which makes surgery even more difficult. In this study, we retrospectively investigated the change in thyroid volume in Graves’ disease that was evaluated on ultrasonography between before and after iodide administration. Eighty-nine patients who received iodide administered (KI(+) patients) and 24 in whom iodide was not administrated (KI(-) patients) before surgery for Graves’ disease were enrolled in the study. The level of free T4 (FT4) significantly decreased and that of thyroid stimulating hormone (TSH) significantly increased after iodide administration. Average thyroid volume also significantly increased for KI(+) patients after iodide administration and 17% of these patients showed a 30% or more increase in thyroid volume. In KI(-) patients who were preoperatively treated only by anti-thyroid drugs, thyroid volume did not change before surgery. Preoperative TSH levels remained below measurement sensitivity in 37 of KI(+) patients, but the average thyroid volume also significantly increased after iodide administration. These findings suggest that thyroid volume in Graves’ disease can increase with iodide administration not only due to TSH stimulation but also due to reasons other than TSH. Surgeons should be careful when preoperatively iodide administering to patients with Graves’ disease, especially when the goiter is large.