The evaluation of patients after severe brain injury is a complex process for the clinician, even with the information provided by a detailed neurological examination. The clinical examination often does not provide sufficient information to fully evaluate these patients due to several factors. Limited and inconsistent motor responses may obscure expression of greater cognitive capacities. More importantly, evaluation of the functional integrity of the cerebral cortical, thalamic and basal ganglia system is poorly indicated by the clinical examination in many patients. Neurophysiological studies provide a complementary set of objective data for evaluating brain-injured patients, as well as predicting and following the course of their recovery. This additional information can be of great importance since vegetative patients may be difficult to distinguish clinically from those in the minimally conscious state. This is important because the latter category of patients may have a significantly better prognosis for recovery in the initial phase of injury. Electrodiagnostic and imaging studies can help the practitioner to determine the degree of preserved and recovering neurological function. In this review we will assess the various neurophysiological studies currently at our disposal to evaluate and follow the clinical course of patients who have suffered severe brain injuries.