Objectives. Although personality is relatively stable over time, there are individual differences in the patterns and magnitude of change. There is some evidence that personality change in adulthood is related to physical health and longevity. The present study expanded this work to consider whether personality stability or change would be associated with better cognitive functioning, especially in later adulthood. Method. A total of 4,974 individuals participated in two waves of The Midlife in the United States Study (MIDUS) in 1994–1995 and 2004–2005. Participants completed the MIDUS personality inventory at both times and the Brief Test of Adult Cognition by Telephone cognitive battery at Time 2. Results. Multiple regression and analysis of covariance analyses showed that, consistent with predictions, individuals remaining stable in openness to experience and neuroticism had faster reaction times and better inductive reasoning than those who changed. Among older adults, those who remained stable or decreased in neuroticism had significantly faster reaction times than those who increased. Conclusions. As predicted, personality stability on some traits was associated with more adaptive cognitive performance on reasoning and reaction time. Personality is discussed as a possible resource for protecting against or minimizing age-related declines in cognition.