A young woman with a normally located and only subtly nodular thyroid gland in the neck was found to have a clinically distinct and radioisotopically "cold" anterior mediastinal mass, which proved to be a benign colloid adenoma. While this constellation of findings usually suggests the presence of a nonthyroidal neoplasm, eg, lymphoma, thymoma, or teratoma, our case illustrates that sequestered benign nodular goiter should also be considered in the differential diagnosis. Clinical clues, such as a nodular thyroid gland, movement of the mass with deglutition, and a family history of nodular goiter, should suggest this possibility. A characteristic computed tomographic appearance may also prove useful in recognition of this rare disorder.