Background: health-related quality of life (HR-QOL) scales are particularly important in older people as global outcome measures for interventions. It is known that people with mild to moderate dementia can provide valid assessments of their own QOL, but it is unclear whether these instruments are useful in those with severe dementia.

Objective: we examined the usefulness of the QOL scale in Alzheimer’s disease (QOL-AD) in people with severe dementia by considering the ability of older people with a Mini-Mental State Examination (MMSE) score of <12 and their caregivers to complete this scale, as well as its construct validity and internal consistency.

Methods: data were collected from people with Alzheimer’s disease and their caregivers using a range of instruments measuring cognition, mood, behaviour, QOL and functional ability.

Results: of 79 participants and their caregivers, 41 (52%) could complete the QOL-AD. Cognition and functional abilities were significantly higher in the completers than in the non-completers (P < 0.001). The QOL-AD showed internal consistency and construct validity as it correlated with ability to look after self, fewer limitations due to physical health, positive mood status and low levels of apathy.

Conclusions: there is evidence for the validity and reliability of the QOL-AD in people with MMSE scores of 3–11, as well as the practicality of administering the scale in this population. The scale is unlikely to generate useful information for people with MMSE scores of <3. QOL does not decrease as cognition worsens. This throws into question most people’s assumption that decreasing cognition worsens QOL. We consider that it may be important to inform the public of this, as living wills are used increasingly in our culture.