Using the Kiel and the Rappaport classifications, a comparative histopathological analysis of 486 cases with non-Hodgkin lymphomas from a prospective study of the Kiel Lymphoma Study Group, still in progress, was performed. The greater part of Rappaport's classical lymphoma entities was found to be inhomogeneous and to include tumors of considerable prognostic heterogeneity, as shown by differences in actuarial survival. Some of the Kiel lymphoma entities have been identified in several lymphoma types of the Rappaport classification, indicating that "translation" of one scheme into the other is difficult or impossible. In addition, centrocytic lymphoma of the Kiel classification may not be homogeneous. On the whole, the Kiel classification appears to be superior to the original Rappaport classification in categorizing the various prognostically diverse types of non-Hodgkin lymphomas.