The diagnosis of Waldenström's macroglobulinemia (WM) requires evidence of bone-marrow infiltration by lymphoplasmacytoid lymphoma and detection of serum monoclonal protein of IgM type. The normal counterpart of the WM malignant cell is believed to be a postgerminal-center B cell. The clinical manifestations and laboratory abnormalities associated with WM are related to direct tumor infiltration and to the amount and specific properties of IgM. Asymptomatic patients should be followed without treatment. When treatment is indicated, the three main choices for systemic frontline treatment are chlorambucil, the nucleoside analogues fludarabine or cladribine and the monoclonal antibody rituximab. There is evidence that high-dose therapy with autologous stem-cell transplantation is effective even in patients with advanced and resistant disease. Patient's age, hemoglobin and serum beta2-microglobulin before treatment are important prognostic variables which correlate with survival.