Definition, classification and prognostic factors in chronic lymphocytic leukemia. Chronic lymphoid leukaemia is characterized by the monoclonal proliferation of mature lymphocytes with or without tumoral syndrome. It is the malignant blood disease most frequent in Occident characterized by a monoclonal lymphocytary proliferation > 5 000/mm3 over one duration higher than 3 months. The prognostic classification of this pathology is at the same time clinical resting on the stage of Binet but also biological. It is very heterogeneous character in term of clinical and biological presentation, but especially of evolution in fact an enthralling and complex pathology with a major current challenge: that to define prognostic factors allowing to establish an evolutionary risk.