Cavernous lymphangioma is a rare mediastinal benign tumor. A 43-year-old woman presented with cough and dyspnea for 1 month. Computed tomography of the chest showed a 3-cm well-circumscribed cystic mass in the posterior mediastinum. At thoracotomy, a cystic tumor in the mediastinum that was adherent to the descending aorta and esophagus was removed completely. The tumor, the cystic space of which was filled with lymph fluid, was diagnosed as cavernous lymphangioma based on pathological findings. Mediastinal lymphangiomas may insinuate into surrounding organs. As incomplete resection can result in recurrence, complete tumor removal should be performed based on accurate preoperative evaluation.