The consequences of a pandemic, both in terms of numbers of patients and the effect on the healthcare system, are likely to precipitate a 'major incident' where special arrangements are needed to manage the system while it is under extreme pressure. It is anticipated that there will be an overwhelming demand for critical care services, not only for respiratory support through mechanical ventilation but also for a full range of care to manage multi-organ failure. Assuming that the next pandemic derives from the H5N1 strain, the epidemiological evidence to date suggests extremely high mortality and, although not precisely quantifiable, a significant risk to health care workers. Both of these will undermine the ability to deliver critical care to influenza patients even before consideration is given to the duty of care to other critically ill patients.