A total of 2192 children with acute lymphoblastic leukaemia who had reached cessation of therapy in complete remission were followed for a median time of 52 months after treatment suspension. Of the 485 relapses observed, 62.3% occurred in the first year off therapy and 68.9% involved the bone marrow. Eight relapses were reported more than 5 years (62-143 months) after treatment withdrawal. Males fared worse than females consistently, experiencing 1.5 times more relapses (P < 0.0001). Thirteen patients died in continuous complete remission, 5 because of non-neoplastic central nervous system complications. There were 11 second solid malignancies, 8 of them in the central nervous system; 9 subjects presented an haematopoietic malignancy after ALL. The projected event-free survival at 8 years is 73%. Twenty-two of the 171 young adults (age > 20 years) were married and 16 have had 21 healthy children. Twenty-four per cent of patients experienced an unfavourable event. Relapses accounted for 93% of failures. Central nervous system late effects and second malignancies were the major causes of non-leukaemic morbidity and mortality.