Deregulation of TCL1 expression can cause the transformation of mature human T and B lymphocytes, and is associated with a variety of human diseases, including T-cell prolymphocytic leukaemia, B-cell chronic leukaemia (B-CLL), B-cell lymphoma and germ-cell tumours [reviewed in [1], [2]]. Here, TCL1A is linked to B-cell chronic lymphocytic leukemia.