Evidence from both animals and humans supports a neuroprotective role of oestrogen. Epidemiological studies showing that oestrogen improves cognitive performance in postmenopausal women, clinical trials showing effects of oestrogen on cognition and data suggesting that oestrogen reduces the risk of Alzheimer's disease (AD) led to the proposal that oestrogen may be effective for improving symptoms or slowing decline in women with AD. Studies evaluating oestrogen as a treatment for AD have been performed with mixed findings. While a few studies have found modest improvements, the results have largely been disappointing. However, many of the studies suffer from substantial methodological problems that leave the findings in question. The role of oestrogen for the prevention or treatment of AD is not yet clear, but large, well-controlled, ongoing trials should provide definitive answers to many questions in the near future.