The outcome of 171 children with ALL who relapsed for the first time after elective cessation of therapy (1-86 mo) and followed over 10 years (median 60 mo; range 1-232 mo) has been evaluated. One hundred and three patients relapsed in the bone marrow (BM), 29 in the testis (T), 21 in the central nervous system (CNS), 14 in the BM plus another site and 4 in other sites. Second remission was achieved in 97% of patients (97% BM, 100% T, 90% CNS, respectively) with reinduction schedules including three or more drugs. All but 4 out of 100 patients who relapsed in the BM received cranial reprophylaxis with intrathecal CT alone or CT plus radiotherapy. Seven patients in second CR underwent allogeneic bone marrow transplantation from an HLA matched sibling. The overall survival was 34% and disease-free survival (DFS) probability at 100 years was 22%. A second relapse was observed in 73% of patients. Forty children are alive in second continuous remission and 24 are alive after a second or subsequent relapse. Patients with isolated T relapse showed a significant better outcome than those with BM or CNS involvement. Most patients (62%) with isolated BM relapse showed a further disease recurrence in BM, and DFS was shorter when relapse occurred within 12 months from off-therapy. Eighty-two patients in second CR stopped the treatment a second time and showed a survival and DFS probabilities, respectively, of 69% and 43%. Thus, children with ALL who relapse after cessation of therapy still have a high risk of further late relapses and should be treated with intensive chemotherapy and CNS reprophylaxis. BMT must be considered for all patients relapsing in the BM within 12 months from off-therapy.