A thyroidectomy involves the surgical removal of all or part of the thyroid gland. Surgeons often perform a thyroidectomy when a patient has thyroid cancer or some other condition of the thyroid gland (such as hyperthyroidism). Other indications for surgery include cosmetic (very enlarged thyroid), or symptomatic obstruction (causing difficulties in swallowing or breathing). One of the complications of "thyroidectomy" is voice change and patients are strongly advised to only be operated on by surgeons who protect the voice by using electronic nerve monitoring.

From http://en.wikipedia.org/wiki/Thyroidectomy