The specific affinity of functioning thyroid tissue for iodine is the rationale for the use of radioactive iodine in tracer doses to study iodine metabolism and the physiology of the human thyroid gland. The pioneer work of Hamilton1and Hertz2initiated this type of investigation. Radioactive iodine was given to a girl 11 years of age in tracer amounts to aid in the preoperative evaluation of a suspected lingual thyroid, subsequently proved to be such microscopically and by radioautograph. This case is reported as another example of the value of radioactive tracer technics in the surgical management of thyroid abnormalities. Feitelberg and associates3have reported the use of radioactive iodine in the study of a lingual thyroid, but their subject did not have operative intervention. Persistence of thyroid tissue at the site of its origin, the foramen cecum at the base of the tongue, is an uncommon