['Leukemia is the leading cause of disease-related death in children, despite significant improvement in survival and modern risk stratification. The prognostic significance of absolute lymphocyte counts (ALC) was evaluated in young patients with acute myeloblastic leukemia (AML) and acute lymphoblastic leukemia (ALL).', 'In all, 171 consecutive de novo cases of AML and ALL, age <or=21 years, were analyzed. Age, initial white blood cell count, cytogenetics, and bone marrow response were compared with lymphocyte, neutrophil, and platelet counts at weekly intervals during induction chemotherapy.', 'ALC is a significant independent predictor of relapse and survival. For example, in patients with AML an ALC on Day 28 of induction (ALC-28) <350 cells/microL predicts very poor survival, with a 5-year relapse-free survival (RFS) of only 10% (hazard ratio [HR] 3.7, P= .003). In contrast, an ALC-15 >350 cells/microL carries an excellent prognosis, with a 5-year overall survival (OS) of 85% (HR 0.2, P= .012). Similarly in ALL, an ALC-15 <350 cells/microL predicts poor survival, with a 6-year RFS of 43% (HR 4.5, P= .002), whereas an ALC-15 >350 cells/microL predicts excellent outcome, with a 6-year OS of 87% (HR 0.2, P= .018). Importantly, ALC remains a strong predictor in multivariate analysis with known prognostic factors.'] Is absolute lymphocyte count a novel prognostic indicator in ALL and AML : implications for risk stratification and future studies?