Based on current prevalence statistics, if you make it into your nineties, then dementias, predominantly Alzheimer's disease (AD), are likely to affect around one in three of us. AD is, in fact, the seventh biggest killer of all ages in the US. This article, by Nigel Borshell, looks at the initial identification of the disease, the various suggestions that have been made as to its causes, treatments that are likely to show promise, and currently hypothesised toxins and possible targets.