This study aimed at the detection of the diagnostic factors and predictors of high probability to develop CNS invasion in cases of acute lymphoblastic leukemia, through studying clinical and laboratory features with emphasis on CSF findings among two groups of patients. Group (A) consisted of 45 newly diagnosed ALL cases without CNS invasion and group (B) consisted of 30 CNS relapsed cases of ALL patients. All cases were subjected to clinical diagnosis, peripheral blood, and bone marrow and CSF examination for total protein, LDH, glucose, chloride, TLC and sIL-2R. Then the results were compared among the two groups.