Objective: To assess the knowledge of four groups of individuals regarding who is legally authorised to consent to health care or research involving older patients.Design: A provincewide postal survey.Setting: Province of Quebec, Canada.Participants: Three hundred older adults, 434 informal caregivers of cognitively impaired individuals, 98 researchers in aging and 136 members of research ethics boards .Measurements: Knowledge was assessed through a pretested postal questionnaire comprising five vignettes that describe hypothetical situations involving an older adult who requires medical care or is (...) solicited for research. The respondent had to identify the person who is legally authorised to provide consent.Results: Nearly 80% of all respondents provided the correct answer when the hypothetical scenario depicted a person who was competent to consent or incompetent but legally represented. Knowledge was worse for the scenario describing a research situation that involved an incompetent adult without a legal guardian.Conclusion: The observed lack of knowledge raises doubts about the ability of current legislation to truly protect the rights of older adults with diminished decision making capacity. It points to the need for educational programmes aimed at increasing public awareness of the legislation put in place for those requiring special protection. (shrink)