Although iron is essential in maintaining the function of the central nervous system, it is a source of reactive oxygen species, which is potentially neurotoxic. Excess iron accumulation has been reported to be associated with many neurodegenerative diseases including Alzheimer disease. Because oxidative damage to neurons is suggested to be an early event of Alzheimer disease, iron deposition in the central nervous system may play a pivotal role in its pathogenesis. In fact, in Alzheimer disease, iron has been demonstrated histochemically to be present in senile plaques and neurofibrillary tangles, the main constituents being amyloid-β and tau, respectively. Since these molecules are key in the pathogenesis of Alzheimer disease, many studies have focused on the relationship of iron with them. However, it has been shown that the oxidative change in neurons is observed before the formation of these pathological hallmarks. This review discusses the suggested role of iron in the progression of Alzheimer disease.