Among small lymphocyte cell disorders, B-chronic lymphocytic leukemia (B-CLL), small lymphocytic lymphoma (SLL), and lymphoplasmacytic lymphoma/Waldenström's macroglobulinemia (LPL/MW) are included. B-CLL patients always have blood and bone marrow (BM) involvement by a CD5+ B lymphocyte. They frequently present with lymphadenopathy and/or hepatosplenomegaly, although in a considerable number of patients, no abnormal physical findings are found. They are prone to develop hypogammaglobulinemia, autoimmune hemolysis, or autoimmune thrombocytopenia. The typical immunophenotype of the malignant cell is CD5+, surface immunoglobulin (slg)+ (weak), CD23+, CD79b-, and FMC7-. Trisomy 12 and 13q deletions are frequent chromosomal abnormalities. The bcl-2 protein is usually overexpressed. SLL patients present with lymphadenopathy, usually generalized. Lymphocytosis is by definition absent and BM involvement, usually nodular, is found in 25% to 50% of patients. The lymph node lymphocytes are CD5+ and have a similar immunophenotype with CLL, but frequently express the LFA-1 adhesion molecule. Patients are at low risk to develop hypogammaglobulinemia, autoimmune hemolysis, or autoimmune thrombocytopenia. LPL/MW patients may present either with an accidental discovery of IgM gammopathy, symptoms related to paraproteinemia, or lymphadenopathy and/or splenomegaly. The BM is frequently involved and a leukemic picture may be found. A monoclonal gammopathy of IgM class is by definition present in MW and is frequently accompanied by hypogammaglobulinemia. Immunophenotypic studies usually reveal a CD5-, slg+ (moderate), cytoplasmic immunoglobulin (clg)+, FMC7+, and CD38+ cell. A significant proportion of cases carry the translocation t(9;14)(p13;q32) involving the PAX-5 gene. All of these disorders may potentially undergo transformation to large-cell lymphoma or Richter's syndrome. Prognostic factors have been extensively studied in B-CLL, but more studies are needed for SLL and LPL/MW. These entities should be differentiated from other B-chronic small lymphocyte cell disorders, particularly when the latter are leukemic.