ADNI: Alzheimer's Disease Neuroimaging Initiative

Inclusion Criteria: Participants will be classified as either MCI patients, AD patients, or normal controls. General Inclusion Criteria will apply to all groups, with specific criteria for each group as described below: General (applies to each category): * Between 55 and 90 years of age (Currently, ADNI sites are only recruiting volunteers age 70-90 among people with no memory problems) * Study partner or caregiver to accompany patient to all scheduled visits * Fluent in English or Spanish * Permitted medications stable for at least 4 weeks prior to screening * Adequate visual and auditory acuity to allow neuropsychological testing * Good general health with no additional diseases expected to interfere with the study * Women must be two years post-menopausal or surgically sterile * Willing and able to complete all baseline assessments, and to participate in the 2-3 year protocol * Willing to undergo neuroimaging and provide DNA and plasma samples as specified * Completed 6 grades of education or sufficient work history to exclude mental retardation * Modified Hachinski score \<=4 * Geriatric Depression Scale \<6 Specific Criteria for MCI and AD patients: * Memory complaint by patient or study partner * Abnormal memory function score on Wechsler Memory Scale (adjusted for education) * Mini-Mental State Exam score between 24 and 30 (MCI) or 20 and 26 (AD) * Clinical Dementia Rating = 0.5; Memory Box score at least 0.5 (MCI) or 1.0 (AD) Exclusion Criteria: * Any significant neurologic disease other than Alzheimer's disease * Abnormal baseline MRI * Presence of pacemakers, aneurysm clips, artificial heart valves, ear implants, metal fragments or foreign objects in the eyes, skin, or body * Major depression, bipolar disorder, history of schizophrenia * History of alcohol or substance abuse or dependency within the past 2 years * Any significant systemic illness or unstable medical condition which could lead to difficulty complying with the protocol * Clinically significant laboratory abnormalities * Residence in skilled nursing facility * Participation in clinical studies involving neuropsychological measures being collected more than one time per year Specific Exclusion Criteria for MCI and AD: * Psychotic features, agitation or behavioral problems within the last 3 months which could lead to difficulty complying with the protocol. Prohibited medications: * Specific psychoactive medications (for example, certain antidepressants, anti-anxiety medications, sleeping pills, etc.) * Warfarin (Coumadin) * Investigational agents