The aim of the study to was evaluate the predictive value of high expression of CXCR4 receptor for extramedullary organ infiltration in childhood ALL. CXCR4 was significantly higher on malignant lymphoblasts in patients with extramedullary organ infiltration than those without extramedullary organ infiltration.Therefore, CXCR4 play an important role in migration of these cells to the circulation & other lymphoid organs. So clinical use of CXCR4 antagonists might positively affect the spreading of the disease.