AChe I have been shown to afford modest benefits on cognition in AD patients. A systematic review by the Cochrane Collaboration states "the practical importance of these changes to patients is unclear" This study's primary objective is to find clinical evidence for the global efficacy of AChE I. The secondary aim is to develop a picture of the natural history of AD. These outcomes will provide a fundamental insight into the progression and treatment of AD aiding the formulation of European guidelines. This is a prospective 2 year observational study which co-ordinates the centralisation of patient data available within the individual centres. It does not require any modification in prescribing practice of participating centres. Patients will be recruited into either a treated or non-treated patient group and reviewed 6 monthly. The primary outcome measure is a deterioration of one level on the clinical dementia rating scale.