Outcome-oriented clinical studies and comprehensive management guidelines for thyroid disease have recently been published. Thyrotoxicosis is a differential diagnostic challenge, and determining the etiology is the most critical step in management. Thyrotoxicosis is referred to as hyperthyroidism when sustained thyroid hyperfunction results in increased thyroid hormone biosynthesis and release from the gland. The most common cause is Graves' disease, but toxic nodular goiters frequently occur in elderly patients. Less common forms include iodine-induced hyperthyroidism, human chorionic gonadotropin-associated thyrotoxicosis and pituitary resistance to thyroid hormone regulation, in which free thyroxine is elevated in clinically euthyroid or hypothyroid patients but thyroid-stimulating hormone is normal to increased. Nonhyperthyroid thyrotoxic states are associated with low radioactive iodine uptake ratios, as seen in the three types of subacute thyroiditis, ectopic hormone production or exogenous ingestion of thyroid hormone. Management of thyrotoxicosis requires lowering of thyroid levels to maintain a euthyroid state. The patient should actively participate in therapeutic decisions. Antithyroid drugs, radioactive iodine and surgery are the principal forms of treatment. Adjunctive therapy may be indicated in some cases. Prolonged follow-up is necessary in all cases.