Allogeneic hematopoietic cell transplantation is widely used to treat adults with high-risk acute lymphoblastic leukemia. The aim of this study was to analyze whether the results changed over time and to identify prognostic factors. Adult patients treated between 1993 and 2012 with myeloablative allogeneic hematopoietic cell transplantation from HLA matched sibling (n=2681) or unrelated (n=2178) donors in first complete remission were included. For transplantations from sibling donors performed between 2008 and 2012, 2-year probabilities of overall survival were: 76% (18–25 years old), 69% (26–35 and 36–45 years old) and 60% (46–55 years old). Among recipients of transplantations from unrelated donors, the respective survival rates were 66%, 70%, 61%, and 62%. In comparison with the 1993–2007 period, significant improvements were observed for all age groups except for the 26–35-year old patients. In a multivariate model, transplantations performed between 2008 and 2012, when compared to 1993–2007, were associated with significantly reduced risks of non-relapse mortality (Hazard Ratio 0.77, P=0.00006), relapse (Hazard Ratio 0.85, P=0.007), treatment failure (Hazard Ratio 0.81, P<0.00001), and overall mortality (Hazard Ratio 0.79, P<0.00001). In the analysis restricted to transplantations performed between 2008 and 2012, the use of total body irradiation-based conditioning was associated with reduced risk of relapse (Hazard Ratio 0.48, P=0.004) and treatment failure (Hazard Ratio 0.63, P=0.02). We conclude that results of allogeneic hematopoietic cell transplantation for adults with acute lymphoblastic leukemia improved significantly over time. Total body irradiation should be considered as the preferable type of myeloablative conditioning.