Objective: Studies of frailty have tended to focus on adverse outcomes. This study aims to develop a short instrument that identifies a positive outcome, namely, the level of well-being in older adults at risk of frailty.Method: 871 older adults (49.4% women; mean age 75.72 years; SD = 8.05) with a frailty risk profile participated in the first wave of the D-SCOPE study. The possible domains of well-being were identified using a bottom-up approach. Exploratory Structural Equation Modeling (ESEM) and multidimensional Item Response Theory (IRT) analysis of 17 items in 4 domains measuring well-being was performed on a calibration sample (n = 435) to develop the instrument. The instrument was subsequently corroborated by confirmatory factor analysis and convergent/divergent relations with relevant external measures in a validation sample (n = 436).Results: The ESEM three-factor solution, with the subdimensions of sense of mastery, meaning in life, and life satisfaction, displayed good fit to the data (RMSEA = 0.070). For each dimension, the three best discriminating items were retained for the instrument following IRT analysis. Internal consistency of these dimensions was good in the validation sample (sense of mastery α = 0.864, meaning in life α = 0.715, and life satisfaction α = 0.782). The confirmatory factor analysis (CFA) three-factor model also showed good fit to the data (RMSEA = 0.064). Small to large zero-order correlations with the external measures were as expected.Conclusions: Using a bottom-up approach, this study developed a short instrument to identify levels of well-being in vulnerable or frail older adults. The instrument can be applied in primary care and prevention programs.