Lesions of the thoracic duct may occur either in the neck or the mediastinum. The majority of lesions that present in the neck consist of chylous fistulae and are secondary to neck surgery. Cysts of the thoracic duct are very rare and are usually reported as a disease entity of the mediastinum. There are only two reported cases in the literature of thoracic duct cysts occurring in the neck. The third case of a thoracic duct cyst located primarily in the neck is reported. Thoracic duct cysts in the neck must be differentiated from other cysts of the neck, because not recognizing the inferior attachment to the thoracic duct, may result in the disastrous consequence of a chylothorax. Diagnosis can easily be made by fine-needle aspiration with biochemical analysis. Computerized axial tomography (CAT) is useful in defining the anatomic boundaries. A weakness in the wall of the thoracic duct, either on a congenital or degenerative basis, has been postulated as the etiology. The natural history of these lesions remains unknown. Smaller lesions may be followed at routine intervals. Larger lesions should be surgically removed because of the possible complications that may ensue as a result of traumatic rupture or inflammation.