This study examined the psychometric properties of the Personal Well-being Index for Adults (PWI-A), a measure of subjective well-being. The study used data from 533 high-ability American college students: honors students and participants in an early college entrance program. In earlier studies using the PWI-A, the instrument appeared to show differences in disaggregated aspects of well-being for these gifted college students. Unfortunately, the careful psychometric examination of the instrument done in this study showed that the PWI-A, as it currently is constituted, did not perform as hoped for assessing changes in the disaggregated aspects of well-being among groups of gifted college students. The single-factor structure of PWI-A showed support for convergent validity, but error correlations indicated lack of support for discriminant validity. The current analysis of the PWI-A scores showed good internal consistency, but the instrument lacked measurement invariance across honors and early entrance students. Four of the seven items exhibited differential item functioning across the two groups. The lack of full measurement invariance indicated room for refinement of the instrument as applied to measuring the well-being of high-ability college students. The results of the current study suggest that to measure accurately the disaggregated well-being of gifted and talented young people, a new, revised, or expanded instrument is necessary. More and diverse items per subscale in a new or revised instrument would allow a more accurate assessment of the specific aspects of the well-being of gifted and talented individuals.