BMT has gained its place in the treatment of childhood leukaemia. Nevertheless, there are still many questions open. In acute lymphoblastic leukaemia children should normally be grafted in 2nd remission (CR). Some high risk cases, however, should probably be grafted in 1st CR. It is not clear whether children with late relapses benefit more from BMT than from renewed chemotherapy. Children with a relapse during maintenance therapy, however, have a better survival rate with BMT. In acute nonlymphoblastic leukaemia certain high risk patients should be grafted in 1st CR but it has still to be shown that BMT is superior to chemotherapy in such cases. It is not clear whether children with a relapse following intensive chemotherapy (such as the BFM-protocols) will benefit from BMT at all. In chronic myelocytic leukaemia, BMT in chronic phase should be performed. Thus, for the first time cure has become possible for this disease. Waiting for acceleration or even the occurrence of a blast crisis decreases the chance of survival after BMT dramatically. Since complications of BMT such as graft-versus-host reaction or severe infections are less frequent in children, relapses remain the main problem after BMT in childhood leukaemia.