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Prevalence is estimated at about 1/7,000. Thyroid ectopia causes around two-thirds of thyroid dysgenesis and is twice as common in females as in males.

Clinical manifestations of thyroid ectopia are often subtle or not present at birth, probably as a result of trans-placental passage of some maternal thyroid hormone or due to the fact that many infants have some thyroid production of their own. Goiter is always absent. More specific symptoms and signs do not develop until several months of age. Common clinical features and signs include decreased activity and increased sleep, feeding difficulty and constipation, prolonged jaundice, myxedematous facies, large fontanels (especially posterior), macroglossia, a distended abdomen with umbilical hernia, and hypotonia. Slow linear growth and developmental delay are usually apparent by 4-6 months of age.

Thyroid ectopia refers to an ectopic location of the thyroid gland. This occurs when a thyroid remnant is found along the normal pathway of the thyroglossal duct, which is the path of the developing thyroid as it descends from the base of the tongue to its final location in the neck. Ectopic thyroid tissue has been found inferior and superior to the hyoid bone and above the thyroid cartilage. No specific mutations have been identified in humans, although mutations in FOXE1 (TTF-2; 9q22) are associated with ectopic thyroid glands in mice.

Imaging studies are required to confirm the diagnosis of ectopia.

Thyroid ectopia is generally thought to be sporadic. However, recent evidence points to the possibility of a genetic component. Around 2% of cases have been shown to be familial.

Without treatment thyroid ectopia results in severe intellectual deficit and short stature.