Introduction : Mediastinal Ectopic Thyroid Gland is a rare entity, accounting for 1% of all mediastinal tumours. Here, we present a rare case of mediastinal mass that was proved to be an ectopic thyroid with normal thyroid function tests and normal thyroid gland in the cervical location. We report in this article two cases illustrating this location. 1st clinical case : 66-year-old woman operated on for benign breast cysts consulted for progressive chest pain. The clinical examination was without abnormalities. The standard biological assessment was normal. Cervicothoracic CT showed two heterogeneous enhancement tissue mediastinal masses, a heterogeneous thyroid gland of normal volume. The surgical procedure consisted of a thymectomy and the anatomopathological study concluded to an intra-thymic ectopic thyroid adenoma. 2nd clinical case : 57-year-old woman consulted for a chronic cough. No anomaly objectified at the clinical examination. The biological assessment including thyroid was normal. The CT scan showed formation of the cervicothoracic orifice whose density evoked a thyroid or parathyroid nodule. The mass was excised and the pathology found a thyroid parenchyma with no signs of malignancy. Comments and conclusion: Transcription factor mutations are implicated in thyroid ectopy. Several locations have been described. The mediastinal localization is exceptional. The presence of a eutopic thyroid is frequently associated with the mediastinal location of ectopia. Clinical-biological euthyroidism is as well. Therapeutically, surgery may be indicated in dyspnea or other disabling symptoms.