OBJECTIVES: : It is important that quality of life (QoL) instruments measure the underlying QoL constructs that are important in their target population. A plethora of QoL instruments designed to measure different QoL constructs exist. However, it is not always clear whether the constructs purportedly measured by these instruments are really that different especially when similar language is used in describing the instruments. This study compares the constructs measured by six instruments focussing on health-related QoL (EuroQoL 5 Dimensions 5 Level (EQ-5D-5L)), older-people-specific QoL (Older People’s Quality of Life brief questionnaire (OPQoL-brief)), social-care-related QoL (Adult Social Care Outcomes Toolkit (ASCOT)), capabilities (ICEpop CAPability measure for Older people (ICECAP-O), mastery (Pearlin Mastery Scale) and self-esteem (Rosenberg Self-Esteem Scale). METHODS: Data on 293 older people from the Australian general population were analysed. Exploratory factor (EFA) and confirmatory factor analysis (CFA), based on polychoric correlation matrices to accommodate the categorical nature of instrument dimensions/domains, were used to identify underlying constructs. Only factor loadings ≥ 0.4 were considered significant. The optimal number of factors to include in the EFA/CFA was determined by examining scree plots obtained from parallel analysis. Interpretation of the EFA/CFA results was based on a ‘varimax orthogonal rotated’ solution due to the exploratory nature of this analysis. RESULTS: Correlations between total/utility scores reflected those between instrument dimensions/domains. The OPQoL-Brief, ASCOT and ICECAP-O total/utility scores all loaded highly onto a common factor (factor loadings: 0.71, 0.70, 0.57, respectively). The ICECAP-O total and EQ-5D-5L utility score also loaded sufficiently onto the same factor (factor loadings: 0.44 and 0.91, respectively) as did the Rosenberg Scale and OPQoL-Brief total scores (factor loadings: 0.48 and 0.69, respectively). Only the Pearlin Scale loaded onto its own separate factors. CONCLUSIONS: The constructs measured by the instruments seem to overlap which raises the potential of their substitutability in some settings.