Primary mediastinal desmoplastic small round cell cancer is an uncommon tumour usually located in the abdomen and pelvis. Here the authors report an extremely rare case of a young male with a primary desmoplastic small round cell tumour in the anterior and middle mediastinum. The patient had non-specific complaints but an abnormal shadow was seen in a routine chest x-ray. He was diagnosed as having mediastinal mass with few lung parenchymal deposits on CT. Mediastinoscopy and guided biopsy revealed desmoplastic small round cell tumour. Desmoplastic small round cell tumour is a rare and aggressive tumour which rarely involves the mediastinum as a primary site. The nature of the lesion and its prognosis were explained to the patient. He was offered chemotherapy and radiotherapy for the tumour management. He refused treatment and left against medical advice.