Following major improvements in prehospital management, comatose patients with severe acquired brain injury are increasingly being admitted to intensive care units (ICUs). The ability to predict the outcome of a comatose or unresponsive patient is a significant challenge for intensive care teams. This is due to the need to provide families with accurate information and to assist in the selection of the most appropriate therapeutic option. To facilitate the decision-making process, clinicians need reliable criteria, particularly in the acute phase of coma. The prognosis of neurological outcome in patients who have not regained consciousness after sedation is a central responsibility of neurologists, clinical neurophysiologists and neurointensivists. Neurophysiological tests, electroencephalogram (EEG) and evoked potentials, provide a noninvasive approach to bedside monitoring of neuronal and synaptic activity in the brain and are the most widely used techniques for assessing altered states of consciousness in critically ill patients. When used in conjunction, these tests can provide valuable insight into the diagnosis and prognosis of these patients.