Abstract
A case of mediastinal thoracic duct cyst is described; it is believed to be the first to be reported in Britain. Five surgically treated cases have been reported but in none was the diagnosis made before operation. Symptoms are caused by pressure of the cyst on the trachea and oesophagus and my be aggravted by eating a fatty meal. Differential diagnosis from other mediastinal tumours, especially bronchogenic cyst and neurofibroma, could perhaps be established before operation by lymphangiography.