Catriona McCullagh is a research fellow currently investigating genetic risk factors for stroke and dementia after stroke. David Craig is a lecturer and specialist registrar studying behavioural symptomatology in dementia. Stephen McIlroy is a geneticist and post-doctoral research fellow studying the genetic and molecular biology of Alzheimer's disease. Peter Passmore (Department of Geriatric Medicine, The Queen's University of Belfast, Whitla Medical Building, 97 Lisburn Road, Belfast BT9 7BL. Tel: 028 9027 2153; fax: 028 9032 5839; e-mail: p.passmore@qub.ac.uk ) is research team leader involved in managing the Regional Centre for Cognitive Disorders, who has also published widely on various aspects of the molecular biology and genetics of Alzheimer's disease.

There is little doubt that dementia is a very common cause of disability and dependency in our society. Since dementia of whatever type is usually more common with increasing age, then as population demographics change, so will the prevalence of dementia. Dementia is a generic term and the objective for clinicians, once dementia is suspected, is to attempt to define the cause. Alzheimer's disease is the most common cause of dementia, and in most centres vascular dementia would feature as the next most common aetiology. In some centres, Lewy body dementia is the second most common cause. Mixed Alzheimer's disease and vascular dementia would also feature high on the list at most centres.