H1N1 had a self-limited respiratory illness; however, if hospitalization was required, 20-36% of patients required admission to the intensive care unit (ICU), and 80% of those patients required invasive mechanical ventilation. The case mortality ranged from 17-40%. In many of these patients, conventional mechanical ventilation strategies were not adequate to reverse their severe oxygenation defects. Adjunctive therapies in addition to lung protective mechanical ventilation strategies are often trialed in patients with oxygenation failure (defined as PaO2 60 mmHg despite FIO2 of 1.0 and optimal positive endexpiratory pressure [PEEP]). Inhaled nitric oxide (iNO) is one such therapy that has shown an improvement in oxygenation in patients with acute respiratory distress syndrome (ARDS). 2,3 In this report, we describe the epidemiologic characteristics, clinical features, treatment, and outcome in the cohort of patients who had ARDS due to H1N1 and were treated with iNO, and we compare their results with those of patients who did not receive iNO. Following approval by the University of Manitoba Biomedical Research Ethics Board, we conducted a retrospective chart review of all patients who presented with confirmed H1N1 and were treated with iNO in the teaching intensive care units at the University of Manitoba’s two adult medical intensive care units. Baseline demographic and clinical data of patients are shown in the Table. After administration of iNO, there was a significant and sustained improvement in the PaO2 and PaO2 /F IO2 ratio at 24 hr, and this improvement persisted throughout the study period (seven days). Three patients in the iNO group eventually required extracorporeal membrane oxygenation due to their profound ARDS. There were two deaths in the iNO group (n = 9) vs ten deaths in the control group (n = 94), 22% and 11%, respectively. Previous work has shown only a transient improvement in these parameters that, in many cases, did not persist past 24 hr. This result is significant as it shows a sustained improvement in oxygenation in these patients with viral pneumonia.