Posterior mediastinum is an atypical localization for the occurrence of ectopic thyroid. We present a case of a 62-year-old man who was admitted to the emergency department with atypical chest pain and dysphagia. The patient was diagnosed as having a true posterior mediastinal ectopic thyroid, which caused esophageal compression. The tumor was completely resected through a sternotomy, with favorable outcome and relief of symptoms.