This is an international trial conducted by three cooperative groups: SFOP (France, Belgium, Netherlands), CCG (USA, Canada, Australia), and UKCCSG (UK and Ireland). Children with mature B-cell lymphoma/leukaemia are stratified into three different risk groups (A, B, C) and receive treatment of progressive intensity. Randomized trials in the 2 biggest groups (B and C) test whether "reduced" therapy is equivalent to standard intensive therapy (LMB-89 B and C) in terms of event free survival. The reason for the modification is to reduce the long term toxicity which includes cardiotoxicity, impaired fertility and secondary malignancy. In group B, the modifications of treatment consists of a reduction of cyclophosphamide in COPADM2 and/or the elimination of COPADM3. In group C, the modification consists in a reduction of the doses in the CYVE courses and the elimination of the last 3 courses of maintenance treatment