We studied pre-transplant minimal residual disease (MRD) in 224 patients (median age 44 years; range 17-65) with acute myeloid leukemia (AML) undergoing allogeneic stem cell transplant (HSCT) in complete remission. MRD was evaluated on marrow samples using multicolor flow cytometry (MFC) and assessment of WT1 gene expression. Both methods showed a strong prognostic value and their combination allowed the identification of 3 groups of patients with different risk of relapse. In multivariate analysis, combined MRD was the only predictor of cumulative incidence of relapse, regardless of donor type, conditioning regimen, first or second CR at HSCT, HSCT year and ELN risk group. Multivariate regression model showed that only negative combined MRD status (p