A 5-year-old male with FLT3 internal tandem duplication (ITD)-positive acute myeloid leukemia (AML) in first complete remission (CR1) develops fever and hypotension 12 days following matched unrelated donor (MUD) bone marrow transplant (BMT) with targeted busulfan/cyclophosphamide/antithymocyte globulin (ATG) conditioning. The gene discussed is FLT3; the disease is acute myeloid leukemia.