Ectopic goiter is rarely seen in the posterior mediastinum. We reported the case of a 54-year-old female who was admitted to our service because of progressive dysphagia, dyspnea on exertion and cough for 3 months. The patient was diagnosed as having a huge posterior mediastinal tumor, which caused tracheal deviation and esophageal compression. The tumor was completely resected through an anterolateral thoracotomy. The final pathological exam confirmed ectopic thyroid tissue. She was discharged with a favorable outcome and relief of symptoms.