Goiters extending into the mediastinum are a commonly encountered medical problem for which treatment is controversial. The frequency of mediastinal goiters increases with age and is more common in women. The predominant causes are benign multinodular goiter and colloid adenoma. Twelve percent of patients with multinodular goiter have some degree of substernal extension. The majority of these patients have symptoms. The most common symptoms are dyspnea, choking, dysphagia, cough, and upper chest pressure. These are generally due to compression of surrounding structures as the goiter passes through the thoracic inlet. Acute respiratory compromise and superior vena cava obstruction have been reported but are usually euthyroid; the incidence of hyperthyroidism is less than 5%. The diagnosis can usually be made by physical examination. Computerized tomography is the most sensitive diagnostic procedure. Mediastinal goiters have a low risk of malignancy. We believe optimal treatment for symptomatic patients is surgical. There is a role, however, for thyroid hormone and radioactive iodine therapy in asymptomatic patients and those who do not desire surgery.