Mediastinal teratoma is an infrequent germ cell tumour and comprises of 1 to 5% of all mediastinal tumours. We report a case of mediastinal mature teratoma in a 12 year old boy who presented to us with persistent non-productive cough, fever and dyspnoea for the past 7 months. Computed tomographic scan of thorax revealed a large anterior mediastinal mass measuring 11.2x9.9x14cm with calcification within. He subsequently underwent a median sternotomy with left subcostal extension (L-incision) and excision of tumour. Histopathology of the tumour revealed a mature cystic teratoma. We would like to report a case of successful surgical management of a large mediastinal mature teratoma in a child.