[Lingual thyroid].
Lingual thyroid is a rare embryological aberration with incidence of 1:100,000. It is an ectopic thyroid tissue. In most cases, it is diagnosed in childhood and young adulthood but frequently around menopause. It appears as a mass on the base of the tongue causing mostly local symptoms often with hypothyroidism, rarely with thrive and mental retardation. Authors describe the features, diagnosis and therapy of lingual thyroid with the case of a 23-year-old woman. They analyze the probable pathomechanism and potential risk of malignant transformation of lingual thyroid. In this case, the diagnosis was described at the age of 17, but therapy or further investigation did not take place then. Six years later the patient visited our surgery with local complaints in euthyroid phase. Since the suppression therapy proved to be unsuccessful, the problem was finally solved by operation.