The invention provides a method of diagnosing Alzheimer's Disease in a subject, by determining the level of at least one miRNA in a sample derived from the subject, wherein a change in the level of the at least one miRNA relative to a suitable control is indicative of Alzheimer's Disease in the subject. Methods for monitoring the course of Alzheimer's Disease, methods of treating a subject having Alzheimer's Disease, and kits for diagnosing Alzheimer's Disease are also provided.