As there was no specific targeted vaccine giving protection against the H1N1 influenza virus available at the beginning of the outbreak, health authorities began to recommend administration of neuraminidase inhibitors to reduce transmission and/or complications. Various studies have suggested that these drugs are also effective in reducing the severity of the infection. 4, 6, 7 We reviewed nationwide Spanish data on hospitalized patients with 2009 H1N1 influenza A in order to: (i) evaluate the frequency of adverse outcomes during hospitalization; and (ii) identify the factors influencing poor/good outcome, including the use of neuraminidase inhibitors shortly after the onset of symptoms.