In general hospitals, decisions are routinely made by health and social care professionals to discharge older people with dementia, who lack capacity, into long-term institutional care. There are few independent procedural safeguards that monitor how those professional ‘best interests’ decisions are made. Instead there is an assumption, implied by the Mental Capacity Act 2005 (MCA), which governs decision-making on behalf of incapacitated adults in England and Wales, that relatives will act as informal caretakers of patients’ interests and will challenge professional decisions where necessary. This article examines whether this is the case in practice and the factors that may prevent relatives from carrying out this safeguarding role effectively. Our findings stem from a qualitative (ethnographic) study which captured observational data on acute and rehabilitation hospital wards in two hospitals within two NHS healthcare trusts in the North East of England. Our results show that relatives struggled to safeguard the rights of incapacitated patients with dementia when professional residence capacity and best-interests decisions were made about living arrangements and relatives were often ill-equipped or unsuitable to carry out this safeguarding role. Without better information-sharing and more robust independent procedural safeguards in the MCA, the rights of older patients with dementia are not being adequately protected during the hospital discharge process.