The 25th of May is World Thyroid Day (WTD). It was introduced by the European Thyroid Association (ETA) in 2008 and has been commemorated annually by all sister Associations: the American Thyroid Association (ATA), the Latin Thyroid Association (LATS), and the Asian Oceanic Thyroid Association (AOTA).

The Day forms part of International Thyroid Awareness Week, promoted and supported by the global, non-profit network of patient organizations known as Thyroid Federation International (TFI).