The safe patient for surgery is the euthyroid patient. Although urgent surgery on unstable thyroid patients can produce good results, it is everyone’s experience that the risk of surgery is increased in those who are dysthyroid. It is therefore critical to the surgeon that the patient about to undergo surgery has as normal thyroid function as possible. Hence, an understanding of thyroid physiology and thyroid function testing is a great asset to every surgeon and especially an endocrine surgeon.