The rapid development of chemotherapy and radiotherapy during the last decade makes an increasing demand for a reliable classification of malignant non-Hodgkin's lymphomas. This is especially important in children since in this age group the lymphomas show a much worse prognosis than in adults. An attempt at a modern classification is offered by the so-called Kiel classification. 38 children with non-Hodgkin's lymphomas previously classified according to Rappaport were re-evaluated according to the Kiel system. Reclassification was technically feasible in 26 patients. There was good agreement on typing between the two independently working cytopathologists. 3 patients proved to be cases of histiocytic medullary reticulosis. Among the remaining patients, a much larger variety of histological subgroups was seen than in the one published paediatric series of Lennert. 17 patients had high-grade malignant lymphomas with lymphoblastic lymphomas predominating. Some clinical correlations not detectable with the Rappaport classification were found using the Kiel system. 6 patients were judged as having low-grade malignant lymphomas but in this group the survival was poorer than expected and 1 patient showed leukaemic transformation. The Kiel classification makes high demands for adequate surgical techniques and preparatory routines. It seems to represent a step forward in the classification of non-Hodgkin's lymphomas but much more experience is needed, especially in children, in order to evaluate its role as a guide to differentiated therapy.