There are measurement difficulties associated with the assessment of health-related quality of life (HRQL) in older people with dementia. The use of proxies is a commonly employed approach to overcome such problems. The research reported in this paper sought to identify, specifically for the EuroQol EQ-5D HRQL instrument, whether construct validity is greater for 'family caregivers' or 'clinicians' as two alternative sources of proxy information for patients with a diagnosis of dementia. This involved the exploration of the strength of the associations between clinical measures of illness severity and EQ-5D data. The data appear to reveal a pattern suggesting that the viewpoint of the proxy (i.e., clinician or family caregiver) is important. The findings suggest that the data provided by clinicians (when compared to data from carers) had higher construct validity for the more observable dimensions of the EQ-5D instrument (i.e., 'mobility' and 'self-care'). Conversely, the data from family carers had higher construct validity for the less observable dimensions (i.e., 'usual activities' and 'anxiety/depression'). Previous research on proxy provision of HRQL data has tended to focus on trying to identify a single proxy. The results of this study suggest that using carefully matched sets of measures and assessment perspectives may produce more valid EQ-5D health state descriptions.