Cholesterol Lowering Agent to Slow Progression (CLASP) of Alzheimer's Disease Study

* Mild to moderate patients with AD who are free of life-threatening disease and who do not require lipid-lowering treatment according to current guidelines. * NINCDS/ADRDA criteria for probable AD. * Mini-Mental-State-Exam (MMSE) score between 12 and 26. * Stable medical condition for 3 months prior to the screening visit. * Age greater than or equal to 50 years, and no upper age limit. * Lives in a community dwelling, not in a nursing home. * Stable doses of (non-excluded) medications with central nervous system activity for 4 weeks prior to the screening visit. * Physical condition acceptable for the study as confirmed by medical history, physical exam, neurologic exam and clinical laboratory tests. * Informant/study partner available and willing to accompany participant to all scheduled visits and complete informant-based assessments and to supervise administration of study medications. * Fluent in English or Spanish. * Modified Hachinski is less than or equal to 4. Exclusion criteria: * Coronary heart disease (CHD) including angina, or peripheral vascular disease including symptomatic carotid artery disease, or stroke or TIA, as these individuals are likely to require treatment with lipid-lowering drugs. * Serious renal disease. * Uncontrolled diabetes. * Triglycerides are greater than 500 mg/dL. * LDL-Cholesterol below 80 mg/dL * Upper limit for the National Cholesterol Education Program (NCEP) guidelines for LDL-Cholesterol is 130-190 mg/dL, depending on age and other cardiovascular risk factors. * Other indication for the need to treat with lipid-lowering drug. * Active liver disease or persistent elevation in serum transaminase. * Active neoplastic disease (skin tumors other than melanoma are not exclusionary; subjects with stable prostate cancer may be included at the discretion of the Project Director). * Use of another investigational agent within 2 months of the screening visit. * History of clinically significant stroke. * Current evidence or history in the past 2 years of seizures, head injury with loss of consciousness and/or immediate confusion after the injury. * Current DSM-IV criteria based diagnosis for major psychiatric disorder including psychosis, major depression, bipolar disorder, alcohol or substance abuse. * Blindness, deafness, language difficulties or any other disability which may prevent the subject from participating or cooperating in the protocol.