The world of chronic lymphocytic leukemia (CLL) research is awash with prognostic markers. However, very few of the current group play a clearly defined role in the pathology of this disease and even fewer represent a tractable therapeutic target. One such marker that fulfils both of these criteria is the integrin CD49d. This molecule been implicated in the capacity of CLL cells to migrate into lymphoid tissues and there is a CD49d blocking antibody, Natalizumab, currently in clinical trials. Here we carried out the largest multi-centre evaluation of CD49d as a prognostic marker in 652 primary CLL samples. We confirm that CD49d is predictive for time to first treatment (P