SIn patients receiving anti-neoplastic chemotherapy, the impact of influenza on the incidence of invasive pulmonary aspergillosis (IPA) remains unknown. We matched data of the Cologne Cohort of Neutropenic Patients (CoCoNut) with records from the Institute for Virology and compared the findings to historical data. During the pandemic, we diagnosed influenza A(H1N1) in five patients with malignancies and febrile neutropenia refractory to antibiotic therapy. Probable IPA was diagnosed in three of these patients on the grounds of typical computed tomography morphology and microbiological results. Three of five patients receiving remission-induction chemotherapy for acute myeloid leukaemia developed aspergillosis although receiving posaconazole prophylaxis. In the 3 years before the influenza pandemic, only 2/77 patients of this group developed infection. Infection with influenza A(H1N1) may increase the risk for invasive aspergillosis in neutropenic patients. Pulmonary aspergillosis is an important additional differential diagnosis in neutropenic influenza patients with pneumonia.