Objective/Background: Chronic lymphocytic leukemia is one of the commonest leukemias affecting adults. CD39 inhibits T-cell and Natural killer (NK) cell responses by hydrolyzing adenosine triphosphate and adenosine diphosphate, suppressing the immune system. We investigated expression of CD39 on CD4+ T Lymphocytes in chronic lymphocytic leukemia (CLL) patients and its relationship with deletion 6q, its association with disease stage and survival. Methods: Thirty CLL patients and 20 matched controls were included in the study. Bone marrow studies with immunophenotyping, CD39, CD38, and ZAP-70, and detection of del 6q by FISH were performed. Results: CD39+ CD4+ T helper cells in CLL patients were significantly expressed compared with the controls (p