This is a prospective Phase II clinical trial of unrelated donor SCT in patients with high risk AML in which KIR typing of the patients and up to 5 potential donors will be available to the treating transplant physician at the time of donor selection. Because not all patients will have a suitably HLA-matched donor that is also mismatched for relevant KIR, there will be an approximately equal segregation into two treatment groups (KIR incompatible and compatible), which will allow comparisons of key SCT endpoints. Methods for coordination among COG member treating centers, the National Marrow Donor Program (NMDP) and its affiliated donor centers, and a KIR typing reference laboratory have been established for this clinical trial. The first aim of the study is to describe clinical outcome data relative to KIR-compatibility and donor-derived NK cell receptor expression. Busulfan, cyclophoshamide and anti-thymocyte glogulin (Atgam) will be used for pre-transplant conditioning. There will be no manipulation of the donor grafts to deplete T cells. Cyclosporine (CsA) and a short course of methotraxate will be given as graft-versus-host disease prophylaxis. A second biological objective is to evaluate NK-cell reconstitution and receptor-acquisition in the recipients, according to variables such as KIR compatibility, and T cell and CD34+ cells dose.