We have analyzed the incidence and risk factors for the occurrence of invasive aspergillosis (IA) among 219 consecutive recipients of an allogeneic hematopoietic SCT after a reduced-intensity conditioning regimen (Allo-RIC). Twenty-seven patients developed an IA at a median of 218 days (range 24-2051) post-Allo-RIC, for a 4-year incidence of 13% (95% confidence interval 4-24%). In multivariate analysis, risk factors for developing IA were steroid therapy for moderate-to-severe graft vs host disease (GVHD) (Hazard Ratio (HR) 2.9, P=0.03), occurrence of a lower respiratory tract infection (LRTI) by a respiratory virus (RV) (HR 4.3, P<0.01) and CMV disease (HR 2.8, P=0.03). Variables that decreased survival after Allo-RIC were advanced disease phase (HR 1.9, P=0.02), steroid therapy for moderate-to-severe GVHD (HR 2.2, P<0.01), not developing chronic GVHD (HR 4.3, P<0.01), occurrence of LRTI by an RV (HR 3.4, P<0.01) and CMV disease (HR 2, P=0.01), whereas occurrence of IA had no effect on survival (P=0.5). Our results show that IA is a common infectious complication after an Allo-RIC, which occurs late post-transplant and may not have a strong effect on survival. An important observation is the possible role of LRTI by conventional RVs as risk factors for IA.