Advances in the treatment of childhood acute lymphoblastic leukemia (ALL) have been striking while results have been less impressive in adults who develop this disease. Obvious differences in a patient's ability to withstand cytotoxic therapy may account, in part, for these findings, but the biologic behaviour of the disease in the two age groups appears to be different; relapses are more frequent and cures less common in adults. In fact, age alone appears to be the most important prognostic factor in ALL. The demonstration of the efficacy of bone marrow transplantation in advanced disease as well as the marked improvements in supportive care and the development of effective high-dose cytotoxic preparative regimens, especially those which use total body irradiation, however, have paved the way for transplantation in first complete remission. Formerly, most adult ALL patients who underwent bone marrow transplant did so in relapse, or in second or subsequent remission. In most studies 40-50% of first remission adult patients attain long-term disease-free survival after allogeneic and autologous bone marrow transplant. Relapses are considerably higher in the autologous transplant group when compared to the allogeneic group, but the latter population may experience increased morbidity and mortality due to graft-versus-host disease and opportunistic infection. These differences may reflect the beneficial graft-versus-leukemia effect in the allograft as well as infusion of autologous leukemia cells in the autograft but neither transplant subtype appears superior. Compared to more conventional approaches, however, transplantation may offer improved disease-free survival, although patient selection appears to be significantly influence outcome. These many inherent biases must be noted when comparing markedly different approaches, e.g. transplant versus conventional therapy. The challenge of demonstrating which therapy is superior for adult ALL patients can only be addressed in a well-designed, prospective, randomized trial.