A right paratracheal mass in a 56-year-old man was found to be a primary intrathoracic goitre. Pathological examination showed nodular hyperplasia with focal lymphocytic thyroiditis. Enlarged mediastinal thyroid tissue may result from extension of a cervical goitre into the chest and is then called secondary or may develop from ectopic thyroid tissue located in the mediastinum and is then called primary. In the latter case blood supply comes from local intrathoracic vessels and no connections with the cervical gland are observed. Differentiation can be made by ultrasonography, CT scanning or radioisotope scanning. Primary goitres are best operated on by way of a thoracotomy as troublesome mediastinal bleeding may occur which is difficult to control from a cervical collar incision.