Pancreatic insulin is transported across the blood–brain barrier to bind to central neurons receptors that can mediate actions of the hormone on cognitive function. In different animal models as well as in healthy humans, a beneficial influence of insulin on sensory processing, learning, and memory has been recently demonstrated. Additional support for this view derives from the investigation of the neuronal mechanisms of memory function. Recent findings of decreased levels of insulin in cerebrospinal fluid and a disturbance of insulin signaling in the brain of patients with Alzheimer's disease (AD) have raised interest in the role of insulin for cognitive impairment. Moreover, findings in cultured neurons hint at an influence of insulin on those cellular and molecular processes supposed to underlie AD pathology. Here, we briefly review the literature suggesting a link between disturbed insulin action in the brain and the development and progress of cognitive dysfunction as well as of neuropathological lesions in AD. Additionally, the potential therapeutic use of insulin in AD patients is discussed. Drug Dev. Res. 56:511–525, 2002. © 2002 Wiley-Liss, Inc.