Acute myeloid leukemia (AML) is an aggressive malignancy for which overall disease-free survival is less than 50%. Manipulation of the immune system is an interesting and promising therapy for AML patients. We aimed to characterize the immune system of AML patients, highlighting the clinical relevance of total bone marrow (BM) lymphocytes and subpopulations. Sixty-six new AML cases diagnosed according to WHO criteria from King Abdullah Medical City, KSA. Analysis of BM lymphocytes and subpopulations was done by flowcytometry. Significantly, high percentages of BM lymphocytes, T cells, and natural killer (NK) cells were detected in the group that achieved complete remission (P values = 0.004, <0.001, and <0.001, respectively). Overall survival (OS) was significantly prolonged in patients with high BM lymphocytes and T cells (P values = 0.047 and P 0.002, respectively). Multivariate analysis indicated that BM T-cell percentage and cytogenetics were independent prognostic factors predictive of OS (HR 4.7, P value = 0.011). BM T-cell percentage constitutes a novel host factor that can be used in combination withcytogenetics to better predict OS. Large-scale multicenter studies are recommended to clarify its role as a predictor of OS and leukemia-free survival.