Allogeneic hematopoietic stem cell transplantation (SCT) has the potential to cure patients with acute leukemia or myelodysplastic syndromes (MDS), but a number of prognostic factors can influence the outcome of transplantation. At present, no transplantation-specific risk score exists for this patient population. We propose a simple scoring system for patients with acute myeloid leukemia, acute lymphoblastic leukemia, or MDS, based on a retrospective analysis of 445 patients undergoing SCT at our institution (divided into training and validation subsets). The score depends on 5 variables: age, disease, stage at transplantation, cytogenetics, and pre-transplantation ferritin. It divides patients into 3 groups of comparable size, with 5-year overall survival of 56% (low risk), 22% (intermediate risk), and 5% (high risk). This prognostic score could be useful in making treatment decisions for individual patients, in stratifying patients entering clinical trials, and in adjusting transplantation outcomes across centers under the new federal reporting rules.