Alzheimer's disease is characterised by the gradual but progressive loss of memory and other cognitive abilities. Pathological features include the accumulation of neurofibrillary tangles, neuritic plaques and &bgr;-amyloid protein within vulnerable regions of the brain. A number of actions of estrogen have the potential to affect brain function and influence the pathology of Alzheimer's disease.Early-onset Alzheimer's disease is a relatively infrequent disorder which is usually inherited in an autosomal dominant manner. However, for late-onset illness, it is likely that several genetic and environmental factors are pathogenetically important.A number of epidemiological studies link postmenopausal hormonal replacement therapy to a reduced risk of developing Alzheimer's disease. Estrogen can affect cognition and mood, and a number of generally small intervention trials suggest that estrogen improves cognitive skills among women with Alzheimer's disease. However, most treatment studies have not been conducted in a methodologically rigorous fashion. There are no firm data on different estrogen preparations and dosages or on the role of progestins in the prevention and treatment of Alzheimer's disease in women, and no data support the use of estrogen for this disorder in men.