Transplant outcome was analyzed in 690 recipients of bone marrow transplants (BMTs) for acute lymphoblastic leukemia (ALL) in first (n = 299) or second remission (n = 391). Actuarial 5-year leukemia-free survival was 42% +/- 9% (95% confidence interval) and 26% +/- 6%, respectively; relapse rates were 29% +/- 9% and 52% +/- 8%, respectively. Five-year leukemia-free survival was 56% +/- 18% in children and 39% +/- 10% in adults (P less than .02) transplanted in first remission. In first-remission adults, non-T-cell phenotype, male to female donor-recipient sex-match and graft-v-host disease (GVHD) were associated with decreased leukemia-free survival; inclusion of corticosteroids in the regimen to prevent GVHD was associated with increased leukemia-free survival. Variables associated with decreased leukemia-free survival after second-remission transplants were age greater than or equal to 16 years and relapse occurring while on therapy. Variables associated with increased probability of relapse were similar for first- and second-remission transplants and included GVHD prophylaxis without methotrexate and absence of GVHD. In first-remission transplants, leukocyte count greater than or equal to 50 x 10(9)/L at diagnosis was also associated with increased relapse; in second remission, relapse while receiving chemotherapy was also associated with increased posttransplant relapse. These data emphasize the importance of both disease- and transplant-related variables in predicting outcome after BMT. They may be used to explain differences between studies, design future trials, and identify persons most likely to benefit from BMT.