The prognosis of the non-Hodgkin's lymphomas is determined by 1. the pattern of origin and spread which can be demonstrated in a staging classification, 2, the histopathological type, and 3. the effectiveness and scope of the treatment methods, particularly radio- and chemo-therapy. In the following paper the Ann Arbor Classification, which was originally conceived of for both disease groups (Hodgkin's and non-Hodgkin's lymphomas), is discussed particularly with respect to the applicability and prognostic evaluation for the non-Hodgkin's lymphomas. The Ann Arbor Classification may in essence reflect the oncological characteristics of the non-Hodgkin's accurately; there are, however, a number of findings with qualitative and quantitative differences which defy integration into the Ann Arbor Classification. The qualitative differences consist of the differing lymphatic and extralymphatic origins and their consequence for spread and prognosis. The quantitative differences refer to the varying patterns of distribution of the different stages of spreading, whereby the dissemination stages in the non-Hodgkin's lymphomas are more dependent on the histological form than is the case with the Hodgkin's lymphomas, and thus must play a greater role in the prognostic evaluation and indication for treatment. Suggestions have been made for a modification of the Ann Arbor Staging Classification for the non-Hodgkin's lymphomas.