A 13-year old Malay school girl who had been apparently normal previously, presented with a three-month history of fever, malaise and loss of weight. She had anemia and raised values for ESR, lactic dehydrogenase, C-reactive protein, ferritin and a positive mantoux test. Her routine chest x-ray showed hilar prominence suggestive of hilar lymph node enlargement. C.T. Scan of the thorax revealed a posterior mediastinal mass, the histopathology of which was suggestive of Ewing's sarcoma. The rarity of the location of the tumour and its unusual mode of presentation prompted us to report this case.