Advances in resuscitation and the advent of modern intensive care techniques to support the circulation challenge the simple definition of death in terms of loss of spontaneous circulation (‘cardiac death’). Instead, death is now better regarded as an irreversible loss of the capacity for consciousness combined with irreversible loss of the capacity to breathe. Since the brainstem is required for both consciousness and spontaneous breathing, irreversible loss of brainstem function (for example after trauma, haemorrhage or hypoxia/ischaemia) defines the state of ‘brainstem death’. Clinical criteria for the diagnosis of brainstem death have been published, although practice varies around the world. Brainstem death lies at the extreme end of a spectrum of disorders of consciousness and is, by definition, permanent. A number of prolonged disorders of consciousness (PDOC) from coma (loss of wakefullness and awareness) through the vegetative state (VS; wakefulness without awareness) to the minimally conscious state (MCS; wakefullness with some awareness) are now recognised. Once potentially confounding conditions have been excluded, the secure diagnosis of VS and MCS is based on expert, multi-disciplinary observation and this must take place over an extended period before permanence can be declared with sufficient certainty. Unlike brainstem death, patients with PDOC may survive for many years without physiological support. The car