Benign teratomas of the thyroid are very rare in adolescence and adults. In this review, we report a case of 14-year-old Korean girl with huge neck mass. She presented with anterior neck enlargement and compression symptom which was rapidly aggravated in 2 months. In physical examination, enlarged and firm right thyroid lobe was palpated and laboratory test of thyroid function was normal. In ultrasonography, right lobe was mainly occupied with a solid nodule size of 44×23×25 mm, showing markedly inhomogeneous hypoechogenicity. As fine needle aspiration cytology was non-diagnostic, lobectomy was done. Histological examination demonstrated that the tumor is benign thyroid teratoma composed of tissue from all three germ layers. When large thyroid nodule is detected in adolescence and malignancy could not be ruled out, final diagnosis should be made with surgical resection. And we should at least attentive for possibility of teratomas when ultrasonographic findings are suspicious.