The aim of this study was to evaluate the impact of marrow blasts at transplant in adult acute myeloid leukemia (AML) patients. We analyzed 478 patients who underwent allogeneic stem cell transplantation (SCT). All patients were divided into five subgroups according to the percentage of blasts: <2 % (n = 361), ≥2 to<3 % (n = 64), ≥3 to <5 % (n = 28), ≥5 to <12 % (n = 11), and ≥12 % (n = 4). After a median follow-up of 59.5 months (range 3.3-125.9 months) for survivors, patients with higher marrow blasts at transplant showed lower overall survival (OS) and disease-free survival (DFS). In multivariate analyses, OS and DFS did not show significant differences with blast counts up to 12 %, compared with blast counts of <2 %; by contrast, the presence of >12 % marrow blasts was associated with significantly poorer OS and DFS. In the separate multivariate analyses by cytogenetic risk group, the impact of >12 % marrow blast on survival outcomes was observed in all risk groups. Thus, pre-transplant bone marrow status is an important prognostic factor for AML patients. In addition, the higher relapse rate in patients with >12 % marrow blasts may provide insights into the tolerable blast cell burden that can be overcome by the graft-versus leukemia effect.