Cystic lesions in the mediastinum constitute one-fourth of all mediastinal masses and are usually identified incidentally. However, hydatid cysts very rarely present in the mediastinum. A 13-year-old male patient was admitted to our hospital because of chest pain and cough. A chest roentgenogram and computed tomography examination found a homogeneous cystic lesion with a size of 7.5 x 7 cm in the anterior mediastinum. Thymectomy was performed following a left thoracotomy in order to complete the pericystectomy. The histological diagnosis was hydatid cyst. No recurrence was observed during 1 year of follow-up.