Abstract: Ectopic thyroid consists of thyroid cells are at sites other than anterior or lateral to the second, third and fourth tracheal rings. Seventy percent of patients with ectopic thyroid, do not have any thyroid tissue at its normal anatomical location. In these patients, ectopic thyroid is prone to functional insufficiency and may come to attention only after compensatory enlargement. If there is no other functioning thyroid tissue, the removal of ectopic thyroid frequently leads to severe hypothyroidism. A patient with a lingual or sublingual thyroid does not require treatment. If patient illustrates hypothyroidism and obstructive symptoms, it is necessary to manage with hormone replacement therapy. If obstructive symptoms can not be decreased, surgical excision is recommended and if the patient does not have eutopic thyroid, the patient will require lifelong hormone replacement therapy. We introduce a 31 year-old female with a firm, nontender mass with smooth surface, mildly mobile mass in both left submandibular and sublingual regions extended to right region. A surgery of the mass of floor of the mouth with salivary gland tumor clinical diagnosis was performed. The histotopathologic examination revealed ectopic thyroid. Because of the lack of eutopic thyroid, she is undertaken hormone replacement therapy. Ectopic thyroid should be considered in differential diagnosis of sublingual mass for avoiding from unnecessary treatments.