This issue of Medical Clinics of North America provides the latest essential updates on thyroid disorders and diseases. Topics covered include the following: thyroid synthesis and physiology; hyperthyroidism; hypothyroidism; thyroid nodules; goiter; differentiated thyroid cancer; subacute, silent, and postpartum thyroiditis; thyroid and pregnancy; thyroid and the elderly; medications and thyroid hormones; thyroid and the heart; thyroid and lipids; and Graves' ophthalmology.