Surgery, the treatment of choice for hyperthyroidism due to nodular goiter, requires an euthyroid state, which is generally achieved with thionamides. Leukopenia is the most serious toxic effect of thionamides, and it causes controindication. We report a 50-year old woman with severe hyperthyroidism and leukopenia, in whom an euthyroid state before thyroidectomy was obtained with the use of therapeutic plasmapheresis. This procedure was carried out immediately before surgery using an intermittent flow separator; three sessions removed a total of 6,300 cc of plasma. Plasmapheresis caused a rapid reduction of both total and free thyroid hormone levels. Thyroidectomy was performed without any complications. Plasmapheresis can be considered a valid and safe method to prepare hyperthyroid patients for thyroidectomy when other therapies are ineffective or counterindicated.