Primary mediastinal hydatid cyst.

An unusual case of primary mediastinal echinococcosis in a young female presented with non-specific symptoms. On examination, she had signs of Horner's syndrome and mild superior vena cava compression. She was operated successfully. The final diagnosis could only be made on the operating table and confirmed by histopathology. Hydatid cyst in mediastinum is uncommon but because of surrounding vital structures and potential of its complete cure should be explored without delay.