Due to the manifold effects of thyroid hormone across virtually all organ systems, the complications associated with thyroid dysfunction are numerous and diverse. The stresses encountered during the perioperative period may exacerbate underlying thyroid disorders, potentially precipitating decompensation and even death. Thus, it is of the utmost importance for the clinician to comprehend the mechanisms by which thyroid disease may complicate surgery and postoperative recovery and to be cognizant of the most effective means of optimizing the status of thyrotoxic and hypothyroid patients perioperatively. This article describes the adverse effects of thyroid dysfunction as they relate to the patient undergoing both thyroid and nonthyroid surgery and recommends treatment approaches aimed at decreasing perioperative risk.