The authors recently experienced a case of lingual thyroid. A 30-year-old-woman came to the hospital on May 9, 1969, having the complaint of the tumor mass in the base of the tongue. On physical examination of oral cavity revealed 2.0×1.5 cm. Mass at the basal region of the tongue. The application of scintigram and RI¹³¹ were performed for the confirmation of the tumor. The scintigram revealed a functioning thyroid gland on the root of the tongue, measuring 4.0×3.0 cm. Concentrated by RI¹³¹, and there was no concentration of RI¹³¹ in the anterior side of the neck. There was not any symptom or sign due to hyperthyroidism, therefore no treatment was given to her.