OBJECTIVE: Having a partner high in optimism is associated with better health in older adults. However, partners, just like individuals, are not static entities and likely change considerably over time. The current study examined whether changes in one person's optimism was associated with corresponding changes in his or her partner's health over a 4-year period. METHOD: We employed a sample of 2,758 heterosexual couples (5,516 individuals; Mage = 65.81, SD = 9.00), married an average of 36.06 years. Median level of education was at least a high school education (13.0% had less than a high school education; 56.1% had a high school education; 30.9% had at least some college education). Both couple members filled out measures of optimism and health twice over a 4-year period. RESULTS: Having a partner high in optimism at baseline was associated with increases in an actor's optimism 4 years later, r = .08, p .05) and partner (rs > .03) changes in optimism were associated with changes in self-rated health and chronic illnesses over time. There was also some evidence for an interaction effect (rs > .03), such that the worst outcomes were experienced among couples in which both members decreased in optimism. CONCLUSION: This is the first study to examine how changes in psychological characteristics are associated with changes in health within and across romantic partners. Possible mechanisms are discussed. (PsycINFO Database Record