OBJECTIVE Immunocompromised patients now benefit from a longer life expectancy due to advanced medical techniques, but they are also weakened by aggressive treatment approaches and are at high risk for invasive fungal disease. We determined risk factors associated with an outbreak of invasive filamentous fungal infection (IFFI) among hospitalized hemato-oncological patients. METHODS A retrospective, matched, case-control study was conducted between January 1, 2009, and April 31, 2011, including 29 cases (6 proven, 8 probable, and 15 possible) of IFFI and 102 matched control patients hospitalized during the same time period. Control patients were identified from the hospital electronic database. Conditional logistic regression was performed to identify independent risk factors for IFFI. RESULTS Overall mortality associated with IFFI was 20.7% (8.0%-39.7%). Myelodysplastic syndrome was associated with a higher risk for IFFI compared to chronic hematological malignancies. After adjustment for major risk factors and confounders, >5 patient transfers outside the protected environment of the hematology ward increased the IFFI risk by 6.1-fold. The risk increased by 6.7-fold when transfers were performed during neutropenia. CONCLUSION This IFFI outbreak was characterized by a strong association with exposure to the unprotected environment outside the hematology ward during patient transfer. The independent associations of a high number of transfers with the presence of neutropenia suggest that affected patients were probably not sufficiently protected during transport in the corridors. Our study highlights that a heightened awareness of the need for preventive measures during the entire care process of at-risk patients should be promoted among healthcare workers. Infect Control Hosp Epidemiol 2014;00(0): 1-9.