Stroke and dementia are closely related. About one patient in ten has dementia before a first-ever stroke, and more than one in three has dementia after a recurrent stroke. Pre-existing dementia is associated with a worse outcome of stroke, and pre-existing cognitive impairment without dementia is associated with a higher rate of institutionalisation within 3 years. In many patients cognitive impairment is due to the summation of the effects of vascular and Alzheimer lesions of the brain.