Unrelated donor (URD) bone marrow transplantation (BMT) in adults can be associated with high non-relapse mortality (NRM). Therefore, factors determining survival in 136 human leucocyte antigen (HLA)-A, B, DRB1-matched adult BMT recipients were reviewed. Fifty-four per cent of patients had chronic myelogenous leukaemia (CML) and 36% had acute leukaemia or myelodysplasia. Graft-versus-host disease (GvHD) prophylaxis was either cyclosporin A (CSA)/methotrexate (64%) or T-cell depletion and CSA/corticosteroids (34%). The probability of donor engraftment by d 45 was 97% (95% CI: 94-100). Incidence of grades III-IV acute GvHD was 18% (95% CI: 12-24) at 100 d, and chronic GvHD was 42% (95% CI: 32-52) at 2 years. At 2 years, 14% (95% CI: 8-20) had relapsed. Multiple regression analysis showed that adverse risk factors for survival were non-CML diagnosis, age > 35 years, diagnosis to transplant time of > 18 months [chronic-phase CML (CML-CP) only]; and grades III-IV acute GvHD. Patients <or= 35 years with early CML-CP had a 2 year survival of 77% (95% CI: 54-100), which compared with a survival in advanced CML patients <or=35 years of 67% (95% CI: 37-97) and 37% (95% CI: 20-54) in non-CML patients. Two year survival for patients > 35 years with early CML-CP was 55% (95% CI: 33-77), 40% (95% CI: 19-61) in advanced CML and 14% (95% CI:1-27) in non-CML. Future efforts should focus on improving the outcome for older BMT recipients, especially those with diagnoses other than CML.