Thyroiditis is an inflammation of the thyroid gland that may be painful and tender when caused by infection, radiation, or trauma, or painless when caused by autoimmune conditions, medications, or an idiopathic fibrotic process. The most common forms are Hashimoto's disease, subacute granulomatous thyroiditis, postpartum thyroiditis, subacute lymphocytic thyroiditis, and drug-induced thyroiditis (caused by amiodarone, interferon-alfa, interleukin-2, or lithium). Patients may have euthyroidism, hyperthyroidism, or hypothyroidism, or may evolve from one condition to another over time. Diagnosis is by clinical context and findings, including the presence or absence of pain, tenderness, and autoantibodies. In addition, the degree of radioactive iodine uptake by the gland is reduced in most patients with viral, radiation-induced, traumatic, autoimmune, or drug-induced inflammation of the thyroid. Treatment primarily is directed at symptomatic relief of thyroid pain and tenderness, if present, and restoration of euthyroidism.