Thoracic duct cysts of the mediastinum are extremely rare. The etiology is related to a congenital or degenerative weakness in the wall of the thoracic duct. Symptoms may arise from compression of adjacent structures. Surgical resection is recommended and allows a definitive histological diagnosis. Postoperative chylothorax is the most frequent complication. We describe a 30-year-old female who presented to us with a history of dry cough and hiccups within the last four months.