Dementia is a neurocognitive disorder which affects brain function over time. The condition may have an insidious onset and diagnosis can sometimes be difficult in the early stages. Subtle behavioural and psychological changes occur which affect social interaction and daily function. Attentional deficits, memory impairment and personality changes might become apparent to individuals or those close to them which can bring them to the attention of their GP or other professionals. There are many causes of dementia, some of which are described here.