Surgical injuries and blunt trauma are the main causes of thoracic duct lesions. Cervical chylous fistula and chylothorax occur frequently after lesions of the cervical portion of the thoracic duct. On the other hand, thoracic duct cyst is a very rare entity, especially in its cervical portion. The authors reported a case of thoracic duct cyst, presenting as an asymptomatic left cervical mass. Diagnosis was suggested by computerized axial tomography and confirmed by histological analysis, after surgical removal of the cyst. After review of the literature, the authors recommended surgical treatment of cervical thoracic duct cysts in order to prevent potential complications as traumatic or spontaneous rupture.