The literature on substernal goiter from the seventeenth century to the present is reviewed. Substernal goiter may be defined as any thyroid enlargement that has its greater mass inferior to the thoracic inlet. Truly ectopic mediastinal goiters are rare, and most substernal goiters arise from and maintain some attachment to the cervical thyroid gland. Patients are generally in the fifth decade of life, and women predominate. Most patients experience dyspnea, stridor, or dysphagia, but 15 to 50% are asymptomatic; symptoms are often positional, and acute stridor may occur. Ten to twenty percent have no cervical mass or tracheal deviation on examination, and virtually all patients are euthyroid. Standard chest roentgenograms are often diagnostic, but computed tomographic or radioactive iodine scans may be helpful. The presence of a substernal goiter in all but the highest-risk patients is an indication for resection, usually through a cervical collar incision; an occasional patient will require sternotomy or thoracotomy. Death or major complications should be rare postoperatively. Substernal goiters are adenomatous and benign, but carcinoma occurs in 2 to 3% and may be occult. Patients should be followed closely, as these goiters may recur.