The results of current treatment of relapsed childhood acute lymphoblastic leukemia (ALL) are discussed, together with some recent developments which (might) influence such treatment. At present more than 95% of children with ALL will achieve a complete remission (CR), and +/- 70% will remain in CR. Nevertheless, 20-30% of the patients suffer a relapse, which implies a less favorable prognosis. However, after intensive treatment a part of these patients will have a prolonged second complete remission: 30-50% of children with a late relapse and 0-20% of children with an early relapse. It is important to prevent the occurrence of a relapse. The identification at diagnosis of patients at high risk for a relapse, and a subsequent more specific and more intensive treatment of these patients might contribute to that goal. Well-known risk factors are briefly mentioned, factors of which the prognostic significances is therapy-dependent. In addition, the treatment of relapsed ALL needs further improvement. Some alternatives to achieve this goal are discussed, including the role of in vitro cytostatic drug resistance testing.