Acute myelofibrosis (AMF), as defined by an acute panmyelopathy associated with marked megakaryocytic hyperplasia and marrow fibrosis, appears to be a stem cell disorder. Even though it is most difficult to distinguish from various myeloproliferative and myelodysplastic disorders as well as acute myelogenous leukemia, it has rarely been reported to terminate as acute lymphoblastic leukemia (ALL). Only five cases have been reported in the literature; two from the pediatric literature and only three from the adult literature. Of the three adult cases, two were defined by light microscopy alone. Among the cases with follow-up (3/5), all died within 2 weeks to 2 months of diagnosis. We report an additional case in an adult; the ALL was defined by morphology, flow cytometric immunophenotyping, and cytogenetic analysis. The interval from diagnosis of AMF to ALL was 3 months. Our patient was treated with standard therapy for ALL, was in complete remission at last follow-up (3 months off maintenance therapy), and represents the only reported case who attained a complete remission. There are too few cases to determine the prognostic significance of termination of AMF in an acute leukemia of lymphoid origin vs. myeloid origin.