In this retrospective study, we analyzed the outcomes of 129 patients who underwent an allogeneic hematopoietic stem cell transplantation (allo-HSCT) and had a history of probable or proven invasive aspergillosis (IA), of whom 57 (44%) received a reduced-intensity conditioning (RIC). Overall, 27 patients with IA progressed after the allo-HSCT (cumulative incidence [CumInc] at 2 years, 22%). The variables that increased the 2-year CumInc of IA progression were (1) longer duration of neutropenia after transplantation; (2) advanced status of the underlying disease; and (3) less than 6 weeks from start of systemic anti-Aspergillus therapy and the allo-HSCT. In addition, (4) conventional myeloablative conditioning increased the risk of progression early after transplantation (before day 30) only, while 3 variables increased the risk beyond day 30 were (5) cytomegalovirus disease; (6) bone marrow or cord blood as source of stem cells; and (7) grades II to IV acute graft-versus-host disease (GVHD). A risk model for progression was generated, defined as low (0-1 risk factors, 6% incidence), intermediate (2-3 risk factors, 27% incidence), or high risk (> or = 3 risk factors, 72% incidence [P < .001]). These findings may help in the interpretation and design of future studies on secondary prophylaxis of IA after an allo-HSCT.