Indolent B lymphoproliferative disorder, chronic lymphocytic leukemia (CLL) represents one of the most common hematologic diseases in the Western world. Although there are many disease development markers known so far, for example, B-cell lymphoma/leukemia (BCL) 2, new ones are needed for better understanding course of the disease. FOXP1 is known to be strongly expressed after B-cell activation. Its essential role in B-cell development suggested that it could also have a role in a various tumor B-cells. We have analyzed 74 bone marrow samples from B-CLL patients for presence of FOXP1 and its gene aberrations in tumor cells. Our results showed presence of FOXP1 protein mostly in the same tumor cells as BCL2 protein, and their specific immunostaining pattern. Diffuse immunostaining pattern of both proteins is present in patients with higher clinical stages of B-CLL and with some other markers that indicate worse outcome of the disease. Thus, FOXP1 and/or BCL2 immunostaining of bone marrow trephine sections could serve as an immunohistochemical marker in B-CLL.