The recently emerged novel influenza A H1N1 virus continues to spread globally. The use of oseltamivir for treatment and prophylaxis of infection is recommended and its use has climbed steeply although there is little data available on its benefit in critically unwell patients with H1N1 influenza. A rare side-effect of oseltamivir treatment reported in post-marketing surveillance is tongue and lip swelling/angioedema. This case report describes the management of a critically ill ventilated patient with severe acute respiratory distress syndrome who developed clinically significant tongue and lip swelling during treatment with oseltamivir.