The EORTC Children Leukemia Group (CLG) is part of the offspring of the EORTC Hemopathies Working Party which in 1978 split into a paediatric and to an 'adult' branch. At that time, the Berlin-Frankfurt-Munster (BFM) designed by H. Riehm for acute lymphoblastic leukaemia (ALL) appeared much more efficacious than all others and the CLG decided to adapt that treatment strategy for its own clinical trials. The main results of these may be summarised as follows:for standard risk patients, the deletion of cyclophosphamide from consolidation and reconsolidation courses does not jeopardise the patient's outcomefor medium- and high-risk patients receiving high-dose methotrexate (MTX), cranial radiotherapy is superfluouswith the dose scheduling of the BFM regimen, E-Coli L-Asparaginase is more efficacious than Erwinia L-Asparaginasethe addition of monthly intravenous (i.v.) 6-mercaptopurine to conventional maintenance chemotherapy is detrimentalthe assessment by quantitative polymerase chain reaction (PCR) of minimal residual disease at completion of induction is feasible in a cooperative setting and can be used as a powerful and independent prognostic factor. The CLG also conducted clinical studies of acute myeloblastic leukaemia. Since 1989, lymphoblastic non-Hodgkin's lymphomas have been treated within the ALL trials. The CLG collaborates with other Groups within the I-BFM Study Group and participants in the meta-analytic studies conducted by the Oxford team by the Oxford Children ALL Collaborative Group.