The demographic characteristics, clinical features, course, and outcomes of severe H1N1 influenza infection requiring intensive care have not been defined rigorously and systematically. While the majority of patients in early reports of critically ill novel influenza A (H1N1) have respiratory involvement, up to 10-20% may present with non-respiratory organ failures, such as shock, seizures, or acute renal failure. The burden of disease and resource utilization of these patients remains largely unknown. The purpose of this surveillance registry is to characterize the demographics, clinical features, outcomes, and resource utilization of patients with H1N1 influenza infection who require intensive care.