Amplitude-integrated EEG (aEEG) has become standard of care in neonates after birth asphyxia for estimation of severity and prediction of outcome. It is also a valuable method for neonates with brain lesions and severe infections as well as for preterm infants for the prediction of outcome. In adult intensive care, interest in aEEG is increasing recently. It has proven beneficial particularly in patients with altered mental state and for the detection and treatment of seizures and monitoring of anticonvulsive treatment efficiency. Of special relevance is the detection of non-convulsive epileptic state, because this condition is associated with an increased risk of in-hospital mortality.