Lingual thyroid is the result of a defective migration of the thyroid anlage occurring between the 3rd and 7th week of gestation. Whereas mutations in the transcription factor-2 (TTF-2) and PAX8 and in the TSH receptor genes (TSH-R) have been reported in a minority of patients with thyroid dysgenesis, the etiopathogeny of the majority of cases, and in particular of thyroid ectopy, remains unclear. The majority of patients with thyroid ectopy are asymptomatic, but obstructive symptoms as well as hypothyroidism have been observed. Hyperthyroidism is an exceptionally rare finding. To our knowledge, only 2 cases have been reported in the literature to date. Herein, we describe an unusual case of thyrotoxicosis related to a nodular lesion in a lingual thyroid. Treatment consisted in restoration of a euthyroid state with thionamide followed by surgical removal of the ectopic gland. The underlying molecular cause of the ectopic lingual thyroid and the toxic adenoma in this case could not be identified. We speculate that abnormally early differentiation of the thyroid gland could interfere with the migration process, a hypothesis yet to be confirmed.