The last years have yielded important new insights into the biological characteristics of chronic lymphocyte leukemia cells, which have lend to modify the diagnosis and prognosis criteria of the disease. The diagnosis is now based on morphology and immunophenotyping of blood lymphocytes, making the bone marrow examination unnecessary. However, detection of a clonal expansion of B-lymphocytes in the blood is far to be synonymous of leukemia, and even less an argument for starting a treatment. Prognosis classifications based on clinical and blood counts are now refined with genotyping and cytogenetics. These new tools should improved the therapeutic strategies in the next future.