 The study is based on the results of five consecutive trials performed by the ALL-REZ BFM study group since 1983. Thus the study meets the criteria of evidence-based therapy, which has been developed over nearly 20 years. Multi-agent chemotherapy in short intensive courses, which are separated by treatment-free intervals, has proved to be a successful form of induction and consolidation therapy. It is followed by preventative or therapeutic cranial irradiation and continuation therapy. A number of risk factors, particularly the time of relapse, site of relapse, and the ALL immunophenotype, allow the stratification of patients into a group that has an acceptable prognosis after treatment with chemotherapy alone and a second group that has a high risk of subsequent recurrence following the achievement of a second remission. The latter group requires further intensification of consolidation therapy by allogenic stem cell transplantation SCT. To date, the indication for SCT has remained unclear for a large and heterogeneous group of patients with an intermediate prognosis. During the precursor study ALL-REZ BFM 96, however, the amount of minimal residual disease MRD determined quantitatively with clonal molecular markers after the second induction therapy element was shown to be a highly significant predictor of relapse-free survival. 