Several lines of evidences support a possible involvement of serum cholesterol in the development of dementia/Alzheimer's disease (AD), with hypercholesterolemia as one of the risk factors that can be targeted by therapeutic interventions. It has also been suggested that statins, prescribed as lipid-lowering drugs to patients at risk for cardiovascular conditions, may be useful in both the prevention and treatment of AD. Currently, conflicting evidences from epidemiological studies indicate a controversial association between dyslipidemia and dementia/AD risk. In randomized clinical trials, virtually no beneficial effect of statin therapy has been observed. On the other hand, in vitro and in vivo animal experiments have revealed that statins suppress amyloid β protein (Aβ) generation. All these findings suggest that statins can be potentially used as preventive or therapeutic agents for AD. In addition, currently the pathophysiological process of AD is thought to begin many years before the diagnosis of AD dementia. Then, statin treatment as well as some disease-modifying therapies may be more efficacious at an early stage of AD including preclinical AD or mild cognitive impairment due to AD.