The impact of the 2009 H1N1-Influenza A (H1N1) pandemic in allogeneic hematopoietic SCT recipients (allo-HSCT) is not yet well defined. Between May 2009 and May 2010, all allo-HSCTs who presented with respiratory symptoms were screened for the presence of the H1N1 virus. Oseltamivir resistance was assessed and chart reviews were performed for all cases. In all, 51 of 248 (20%) allo-HSCT recipients followed at our outpatient clinic were screened. We identified 10 patients with H1N1 infection. Close contact with children was the most commonly suspected mode of transmission. Upper and lower respiratory tract infections were present in eight and five patients, respectively. Lymphopenia (<1 G/L) was the most frequent biological abnormality. High immunosuppression was responsible for severe infection requiring mechanical ventilation associated with prolonged viral shedding in three patients who had significant comorbidities and GvHD. Two of them developed an oseltamivir-resistant strain and both patients died subsequently despite intensive therapy, resulting in a case fatality rate of 20%. In conclusion, although most allo-HSCTs had mild symptoms from H1N1 infection, severe immunosuppression and emergence of oseltamivir resistance were likely responsible for a substantial morbidity, further supporting the need for vaccination and monitoring of close contacts, especially children.