Background: Although advance directives may seem useful instruments in decision-making regarding incompetent patients, their validity in cases of dementia has been a much debated subject and little is known about their effectiveness in practice. This paper assesses the contribution of advance directives to decision-making in the care of people with dementia, with a special focus on non-treatment directives and directives for euthanasia. Methods: The relevant problems from the ethical debate on advance directives in cases of dementia are summarized and we discuss how these relate to what is known from empirical research on the validity and effectiveness of advance directives in the clinical practice of dementia care. Results: The ethical debate focuses essentially on how to respond to the current wishes of a patient with dementia if these contradict the patient's wishes contained in an advance directive. The (very limited) empirical data show that the main factors in medical decision-making in such cases is not the patient's perspective but the medical judgment of the physician and the influence of relatives. Insight into the experiences and wishes of people with dementia regarding advance directives is totally lacking in empirical research. Conclusions: Ethics and actual practice are two different worlds when it comes to approaching advance directives in cases of dementia. It is clear, however, that the use of advance directives in practice remains problematic, above all in cases of advance euthanasia directives, but to a lesser extent also when non-treatment directives are involved. Although generally considered valid, their effectiveness seems marginal. Further empirical research into the (potential) value of advance directives in dementia care is recommended. © International Psychogeriatric Association 2009.