There are approximately 400 reported cases of lingual thyroid (LT) with a clear cut prevalence in paediatric age. These glands are probably quantitatively deficient and function at marginal levels. Thyrostimulating hormone (TSH) causes hypertrophy producing local symptoms and in younger patients may induce dangerous obstruction. The presumptive diagnosis is usually made by indirect laryngoscopy and thyroscintigraphy. The authors describe a case of LT in a middle aged patient in whom the anomaly remained undiscovered, being without local symptoms, and permitting a normal life. The discovery was made possible by the development in the last four years of a progressive, frank hypothyroidism, probably induced by silent thyroiditis into the ectopic gland.