Over recent years practitioners are increasingly being asked to attend to, or to provide treatment for, adult patients with some degree of mental illness, either in their homes or in the dental surgery. Demographic changes, an ageing population with increasing incidence of dementia, and the philosophy of 'care in the community' for those with long-term mental health problems will ensure that such requests will continue. Such requests present the practitioner with a number of ethical and legal problems. this series of papers looks at the legal issues that arise by reference to case scenarios in this area of 'special needs' dentistry. This first paper deals with the issue of consent, and the legal duty of care that arises on the part of the dentist when attending a patient who is unable to consent to treatment.