Low-grade non-Hodgkin's lymphomas are characterized by a low proliferative activity and prolonged clinical course. Most of them reveal distinct cytogenetic and molecular aberrations, such as the translocation t (14; 18) in centrocytic/centroblastic or follicular lymphomas, which is combined with an overexpression of the bcl 2 oncogene or the translocation t (11; 14), which is associated with a deregulation of the PRAD 1 gene and is mainly found in centrocytic or mantle-cell lymphomas. The therapy of low-grade non-Hodgkin's lymphoma depends on the extent of the disease. In early stages I and II, in which only 15 to 25% of low-grade lymphomas are diagnosed, radiotherapy represents the treatment of choice and may be applied with curative intention. The appropriate treatment of more advanced stages III and IV is a matter of controversial debates. Currently, it still seems justified to watch the natural course of the disease and to start therapy not before the occurrence of B-symptoms, hematopoietic insufficiency or progression of lymphoma. Intensification of initial cytoreductive chemotherapy does not result in a prolonged survival or a higher remission rate. However, maintenance therapy with interferon alpha following successful initial cytoreductive chemotherapy appears to have a favorable impact on disease-free and possibly also overall survival. New perspectives result from the introduction of new cytostatic compounds and the purine analogues in particular as well as the development of effective immunotoxins and antibody-conjugated radio-isotoes. Furthermore, myeloablative radiochemotherapy followed by autologous bone marrow or peripheral stem cell transplantation provides a promising approach with curative potential even in advanced stages of the disease.