The patient is a 23 year old female who presented with complaints of dyspnoea and dry cough. CT thorax showed a large, ill defined heterogenous soft tissue density mass lesion involving mediastinum measuring 15cm x 5 cmx 14 cm. Bone marrow aspirate showed a diffuse infiltrate of atypical lymphoid cells /blasts (71%) which are 14-18 microns in size having high nucleo-cytoplasmic ratio,immature chromatin,inconspicuous nucleoli and scant bluish cytoplasm along wih prominent cytoplasmic vacuoles in many cells resembling Burkitt's. However, flowcytometry analysis showed a T-ALL phenotype with cyto and surface CD3, CD4,CD8, CD99, CD7,CD1a,CD2 and CD5. The findings were confirmed by a biopsy from cervical lymph where the tumour cells were positive for CD3,Tdt with a MIB index of 90% and a final diagnosis of T lymphoblastic lymphoma/leukemia was made