BACKGROUND Bone marrow aplasia preceding acute lymphoblastic leukemia (ALL) is a rare condition that usually affects children. The ALL generally follows the recovery of normal blood counts and most commonly occurs within 6 months of the onset of aplasia. The case of a patient with severe aplastic anemia is reported in whom ALL developed 15 months after the initial diagnosis of aplastic anemia. A literature search found 23 cases of ALL after a period of aplasia or hypoplasia. This patient's disease, however, was different from all previously reported ones. The severe aplasia lasted 15 months before being followed by ALL. There was no recovery of blood counts before the onset of ALL. METHODS A review of the literature found 23 case reports in which aplasia or hypoplasia preceded ALL; these patients also had pancytopenia of the peripheral blood. Excluded from this review were patients whose bone marrow was hypoplastic, but who did not have pancytopenia because these did not have "aplastic anemia" as their initial disease. RESULTS Analysis of the reported patients showed that most were girls 10 years of age or younger. There was an overwhelming prevalence of fever, which in several instances, might have had an infectious cause. ALL most commonly occurred within 6 months of the aplasia and usually followed the recovery of normal blood counts. CONCLUSIONS Patients with ALL after a prolonged period of aplasia have several common characteristics including female sex, young age, and the prevalence of fever, often associated with an infectious illness. ALL usually follows the recovery of blood counts and occurs within 6 months of the onset of aplasia. The pathophysiology of this patient's disease(s) is still unclear. He could have had two unrelated disorders or a two-step leukemic process that followed a stem cell "insult." This patient had an antecedent hepatitis A infection 3 months before aplasia occurred. However, the authors were unable to identify with certainty any other event that might have caused additional bone marrow injury.