Dementia is defined as an impairment in more than one cognitive domain below the premorbid level, severe enough to interfere with activities of daily living. The most common form of dementia is Alzheimer's disease affecting approximately 5% of the population above the age of 65. The clinical symptoms of dementia are divided into three groups including cognitive deficits, behavioral symptoms and deficits in activities of daily living. The diagnosis of dementia can be subsumed into two steps, the diagnosis of dementia syndrome (differentiation from non-dementia) and differential diagnosis as to the cause of dementia. The diagnosis of dementia is made clinically, auxillary investigations may help with regard to the underlying cause. There is a long list of potential causes of dementia, it is useful to group these into two broad categories: primary degenerative dementias and symptomatic forms of dementia. In the latter category one can distinguish diseases which directly affect brain tissue, conditions which inflict mechanical effects on the brain and conditions which affect the functioning of brain indirectly.