Performing not only related but also unrelated allogeneic stem cell transplant (allo-SCT) for adult Philadelphia chromosome-negative acute lymphoblastic leukemia [Ph(-) ALL] during first complete remission (CR) may be a potent therapeutic strategy for long-term survival. The survival times after related or unrelated allo-SCT may be comparable, but different background risk factors arising from differences in donor types should be recognized to improve the outcome of allo-SCT. In addition, age should be considered as an important factor. In adolescents and young adults, for whom intensified pediatric protocols show promise for improving outcomes, minimal residual disease may be helpful for making the decision to conduct allo-SCT during first CR. For older adults, however, reduced intensity conditioning (RIC) could expand the indication for allo-SCT for Ph(-) ALL in CR. Since the non-relapse mortality of allo-SCT remains significantly high compared with that of conventional chemotherapy, careful selection of patients is mandatory. However, it is crucial not to miss the correct timing of allo-SCT, given that the prognosis of relapsed ALL is very dismal. After close consideration of donor type, patient age, response to chemotherapy and appropriate timing, the outcome of allo-SCT for adult Ph(-) ALL could be improved.