We investigated the prognostic impact of absolute lymphocyte count (ALC) following induction chemotherapy in newly diagnosed adult acute lymphoblastic leukemia (ALL). Patients with ALC ≥350 cells/μL at day 28 had a median overall survival (OS) of 47.4 months when compared with 17.6 months for those with an ALC <350 cells/μL (HR = 1.98, P = 0.007). Among patients who achieved a complete remission, median event-free survival (EFS) for those with ALC ≥350 cells/μL on day 28 was 42.1 months when compared with 13.9 months in those with ALC <350 cells/μL (HR = 2.08, P = 0.006). In multivariable analysis, the ALC on day 28 (<350 cells/μL vs. ≥350 cells/μL, P ≤ .0004 for OS and EFS) along with WBC at diagnosis (≤6.0 or >30.0 K/μL vs. >6.0-30.0 K/μL, P ≤ 0.002 for OS and EFS) and cytogenetics (abnormal vs. normal, P = 0.002 for OS and P = 0.02 for EFS) were independent prognostic factors of both OS and EFS. Combining these three factors segregates patients in three well-defined risk groups. These data suggest that ALC can be used in combination with other prognostic features to better predict outcome and that targeting the immune system to improve ALC may be a worthwhile strategy in ALL. Am. J.Hematol. © 2012 Wiley Periodicals, Inc.