This article is focused on the mechanisms underlying primarily ischaemic/reperfusion brain injury in both the term and premature infant. Although the mechanisms involved include similar initiating events, principally ischaemia-reperfusion, and similar final common pathways to cell death, particularly free radical-mediated events, there are certain unique maturational factors influencing the type and pattern of cellular injury. We will therefore initially describe the physiological and cellular/molecular mechanisms of brain injury in the term infant, followed by the mechanisms in the premature infant. Copyright 2000 Harcourt Publishers Ltd.