Background : Allogeneic bone marrow transplantation (BMT) offers the greatest chance of cure for most patients affected by acute myeloid leukemia (AML). Persistence of disease or high levels of pre BMT minimal residual disease (MRD) have been reported to predict disease relapse after BMT. WT1 expression levels and multicolor flow cytometry (MFC) are widely used as markers of MRD. We recently reported that combined evaluation of MRD by WT1 and MFC after induction therapy can predict relapse risk in AML patients. Aims : The aim of the present study was to apply the same MRD assessment in pre BMT setting to evaluate its reliability in predicting relapse. Methods : We retrospectively analyzed BMT outcome of 66 AML patients with both WT1-based and MFC-based MRD evaluation on bone marrow samples before transplant. Median age at transplant was 44 years. Forty-one were transplanted in first and twenty-five in second or subsequent complete remission. Induction therapies included fludarabine-containing regimens or standard ara-C and daunorubicin schedule (3+7). Median follow-up was 44 months (range 0-119 months); pre-transplantation evaluations were performed at a median of one month before transplant (range 1-3). Disease-free survival (DFS) was calculated from the time of transplantation until last follow-up or documented leukemic relapse. Overall survival was calculated from the time of transplantation to the last follow-up or death for any cause. All causes of death not directly due to relapse or progression of leukemia were considered as non-relapse mortality. A positive MFC MRD was defined by the presence of no less than 25 clustered leukemic cells /10 5 total events (threshold of 2.5x10 -4 residual leukemic cells) at four-color flow-cytometry. Real-time PCR for WT1 was performed on DNA Engine 2 (Opticon®, MJResearch®). WT1 copy number/Abl copy number 500x10 4 was used as cut-off value for high WT1 expression. Results : Twenty-five relapses (37.9%) were observed. Median DFS was 31 months. Our analysis shows that the probability of relapse was significantly influenced only by disease status (first or subsequent CR) and MRD status at transplantation. Specifically, MFC-MRD was the strongest predictor of longer disease free survival (p Conclusion: pre BMT MRD evaluation by WT1 and MFC on bone marrow samples is a reliable tool to predict relapse risk. Patients with negative pre-BMT MRD have a significantly longer DFS and OS, while MRD positive patients by both methods display a higher risk of relapse. Patients at higher risk of poor outcome should undergo a more stringent program of post BMT evaluations, in order to detect disease relapse earlier and might be candidate for pre-emptive therapeutic interventions aimed at delaying or avoiding AML reoccurrence. Disclosures No relevant conflicts of interest to declare.