Though survival of children with acute lymphoblastic leukaemia (ALL) has improved, relapse remains a leading cause of mortality in childhood cancer. Given the rarity of the disease, only a large international cooperative group can recruit sufficient patients for prospective studies with specific questions in biologic subgroups. Under the umbrella of the I-BFM SG all relevant mainly European study groups are creating the worldwide largest Study for Children with Relapsed ALL (IntReALL 2010). The aim is to develop optimized standard treatment as platform for systematic randomized phase II and III studies on the most promising new and targeted agents. An adequate trial structure, an optimized web based database, and standardized diagnostic methods need to be established.Patients are stratified into a standard (SR) and a high risk (HR) group according to established factors. For SR patients, the best available treatment protocols ALL-REZ BFM 2002 and ALL R3 are randomly compared, and the additional effect on survival of the humanized monoclonal CD22 directed antibody epratuzumab is investigated. HR patients who have unsatisfying remission rates will receive an intensified induction with the proteasome inhibitor bortezomib randomly combined with standard induction therapy. IntReALL 2010 allows for comprehensive tumour banking and systematic biologic research in subgroups with correlation to clinical outcome. SMEs will be involved into project management, data base development, and pharmaceutical and biotechnological research to ensure innovation in the respective areas. IntReALL 2010 is embedded in a network of European academic structures relevant for childhood cancer. It will be a cornerstone of drug development in childhood leukaemia and the only trial with the potential for well powered phase III studies in this indication. IntReALL 2010 will harmonize ALL-relapse therapy, establish highest diagnostic and therapeutic standard and improve survival of children with ALL.