Thirty-two patients with poor risk acute lymphoblastic leukaemia in first complete remission received bone marrow transplants (BMT) from fully matched family donors. Their ages ranged from 7 to 41 (median 23) years. Nine patients were aged 16 years or less. Patients were selected for BMT because they had risk factors for relapse with standard treatment approaches. In particular the children who were selected for BMT had presenting blast counts of greater than or equal to 90 x 10(9)/l or null immunophenotypes. The overall disease-free survival was 50% with a relapse risk of 31% at 9 years. Patients aged less than 16 years had a much lower risk of both graft-related disease and relapse than did older patients (disease-free survival 89% for those aged 7-16, 48% for those aged 17-26, 24% for those aged 26-41). We conclude that selection of BMT for young patients with poor risk features is entirely justified but that the prognosis for older patients is poor even after BMT.