BACKGROUND: Obtaining informed consent to treatment is an important medical-legal and clinical aspect of neurological practice. REVIEW SUMMARY: This review discusses the doctrine of informed consent and its role in neurological practice. We first provide an overview of the informed consent doctrine and discuss its historical origins and current modern form. The three component elements of informed consent--being informed, voluntary, and competent--are presented, with a focus placed on the competency element. The increasingly important role of informed consent in everyday neurological practice is profiled, with particular emphasis on patients with dementia. Recent empirical research is presented on loss of consent capacity (competency) in patients with Alzheimer's disease and Parkinson's disease. Finally, a conceptually based approach to clinical assessment of competency is presented to assist neurologists dealing with these issues. CONCLUSIONS: The increasing prevalence of patients with neurodegenerative disorders in neurological practice heightens the importance of obtaining valid informed consent to treatment.