To explore construct validity and reliability of the Thriving of Older People Assessment Scale.The concept of thriving emphasizes person-environment interaction in relation to well-being. The Thriving of Older People Assessment Scale has been developed and evaluated as a self-report and proxy scale based on the theory of thriving.Cross-sectional survey design.The Thriving of Older People Assessment Scale was completed by a sample of 259 residents, 146 family members and 52 staff from 13 long-term care facilities in Norway and Sweden. Data were collected between April 2010-December 2011. Exploratory factor analysis was applied to explore construct validity in terms of factor structure and dimensionality of the 32-item scale in relation to the thriving theory. Reliability was explored through internal consistency estimation using Cronbach's alpha and through homogeneity evaluation using corrected item-total correlations.Exploratory factor analysis resulted in five factors (subscales) that corresponded meaningfully with the thriving theory and were labelled 1: Resident' attitudes towards being in long-term care; 2: Quality of care and caregivers; 3: Resident engagement and peer relationships; 4: Keeping in touch with people and places; and 5: Quality of the physical environment. The scale had satisfactory internal consistency and homogeneity estimates.The 32-item Thriving of Older People Assessment Scale can be regarded as construct valid and reliable. Its factor structure corresponded logically to the thriving theory and its factors showed satisfactory internal consistency and homogeneity. Nevertheless, the TOPAS would benefit from further testing in other populations and contexts.