This invention relates to methods for diagnosing Alzheimer's Disease (AD) by determining the level or function of insulin, insulin-like growth factors, their receptors and/or their downstream signaling molecules. The invention further relates to methods for the treatment of AD by administering an insulin agonist and an insulin-like growth factor agonist. The invention additionally provides an animal model of AD and methods of screening for agents useful in the treatment, amelioration, or prevention of AD.