Ischemic stroke is characterized by the disruption of cerebral blood flow, which produces a central core of dead neurons surrounded by a penumbra of damaged but partially functional neurons. Many factors are associated with such brain injury, including excitotoxicity and free radicals. Recent clinical studies have shown that high plasma ferritin levels are detrimental in acute ischemic stroke. As an iron-storage protein, ferritin can act both as a scavenger and as a donor of free iron, which is a source of hydroxyl radicals. Following disruption of the blood-brain barrier, the ferritin and the free iron that have accumulated in endothelial cells in brain capillaries, together with plasma ferritin, can enter the penumbra. Iron-dependent oxidative stress in the penumbra can lead to necrosis and further neurological deterioration following ischemic stroke. An excess of iron should be considered pathological in the ischemic brain. Therapeutic strategies for ischemic stroke should attempt to restore brain function within the penumbra. Consequently, the iron content of systemic stores should be measured, and anti-oxidant treatment should be considered when it is excessive.