Cerebral insult is a generic term which includes many causes of altered cerebral function. Neurophysiological investigations, closely integrated with clinical and metabolic studies, should begin at an early stage after any such insult (namely in the first few hours) to provide information on the type, severity and evolution of latered brain function. The present contribution is based on prospective studies on 200 children with closed head injuries and 500 children who had been resuscitated following cardiocirculatory or respiratory arrest. In addition to electroencephalography, other neurophysiological investigations may be carried out whenever necessary including electroretinography, evoked potential studies and polyelectromyography at the patient's bedside, whether or not in the intensive care situation. The rapid evolution of metabolic events and of both clinical and neurophysiological features characterizes the acute initial phase, in marked contrast to the more static features of long term sequelae to a cerebral insult. Experience over the past 25 yr has shown that no rule is applicable to every case because of the diversity of individual circumstances. However, a well planned early neurophysiological assessment after insult to the central nervous system has given reliable prognostic criteria for the subsequent management of each patient and for the evaluation of any complications during the first few weeks of treatment.