The preoperative preparation of hyperthyroidism requires the selective use of various drugs. As in the past, Plummer's iodine therapy takes precedence. Thyrostatics or beta receptor blockers, on the other hand, are only used in selected cases. The aim of preoperative preparation is euthyroidism. It is most rapidly and safely attained with Endoiodin (prolonium iodide) or combination of Endoiodine plus beta receptor blokkers. Thyrostatics appear to be less suitable for preparation, because they have a slow onset of action. Moreover, thyrostatics lead to densifications and adhesions of the thyroid gland capsule to the surrounding tissue, so that the preparation becomes complicated. 254 patients with hyperthyroidism and decompensated toxic adenoma were surgically treated without complications as a result of preparation with Endoiodin.