In recent years considerable advances have been made in the treatment of non-Hodgkin lymphomas, yet the results are not so impressive as the progress in treating patients with Hodgkin's disease. This may be partly explained by the lack of standardized histological classification and staging procedures, which are responsible for our incomplete knowledge of the pathogenesis and clinical course of the different lymphoma types. The most important histological classifications and procedures for adequate staging are presented. To the extent of present knowledge the initial manifestations and pathways of dissemination are discussed. So far established data makes it possible to lay down therapeutic principles which differ according to stage and histology. Loco-regional stages should be treated by radiotherapy alone. In advanced phases combined cytotoxic chemotherapy is for the most part the accepted form of treatment. While in prognostically favorable histological types a mild regimen may suffice, aggressive cytotoxic regimens should be preferred in treating unfavorable histological types. Treatment modalities combining radiotherapy and chemotherapy are still experimental. Hodgkin's lymphomas and diffuse histiocytic lymphomas in stages III and IV are potentially curable by chemotherapy.