OBJECTIVE To compare efficacy of intensive postremission chemotherapy with allogeneic bone marrow transplantation in adults with acute lymphoblastic leukemia (ALL) in first remission. METHODS Retrospective comparison of two cohorts of patients. METHODS Chemotherapy recipients were treated in 44 hospitals in West Germany in two cooperative group trials; transplants were done in 98 hospitals worldwide. METHODS Patients (484) receiving intensive postremission chemotherapy and 251 recipients of HLA-identical sibling bone marrow transplants for ALL in first remission. Patients ranged from 15 to 45 years of age and were treated between 1980 and 1987. RESULTS Similar prognostic factors predicted treatment failure (non-T-cell phenotype, high leukocyte count at diagnosis, and 8 or more weeks to achieve first remission) of both therapies. After statistical adjustments were made for differences in disease characteristics and time-to-treatment, survival was similar in the chemotherapy and transplant cohorts: Five-year leukemia-free survival probability was 38% (95% CI, 33% to 43%) with chemotherapy and 44% (CI, 37% to 52%) with transplant. No specific prognostic group had a significantly better outcome with one treatment compared with the other (6% for the difference; CI, -3% to 15%). Causes of treatment failure differed: With chemotherapy, 268 (96%) failures were from relapse and 11 (4%) were treatment-related; with transplants, 43 (32%) failures were from relapse and 92 (68%) were treatment-related. CONCLUSIONS These results suggest that bone marrow transplants currently offer no special advantage over chemotherapy for adults with acute lymphoblastic leukemia in first remission.