Children with high risk or relapsed acute lymphoblastic leukaemia (ALL) can benefit from allogeneic haematopoietic stem cell transplantation (SCT). To reduce transplantation-associated complications, the BFM study group, the IBFM study group and the PD-WP-EBMT initiated a prospective cooperative multicentre trail for paediatric ALL patients with an indication for allogeneic stem cell transplantation. Four-digit high-resolution HLA typing for all nonsibling donors, standardised GvHD prophylaxis and therapy, uniform conditioning regimen and minimum standards for supportive care should reduce not only treatment-related mortality but also ameliorate late effects for young patients. Furthermore, the prospective evaluation aims to assess the role of haematopoietic SCT in comparison to chemotherapy to enable valuable treatment recommendations for further decisions.