We performed a retrospective observational study to examine the incidence of invasive aspergillosis (IA) among allogeneic hematopoietic stem cell transplant (HSCT) recipients, according to whether patients received at least 1 week of voriconazole prophylaxis. We report no cases of IA among 92 HSCT recipients who received voriconazole prophylaxis compared with a 10% (23/223) incidence among those receiving other systemic antifungals for prophylaxis (P < .0005).