Guided by a life-span developmental systems approach, this study examined links between self-esteem assessed over 25 years and adaptive interaction and relationship risk at midlife using data from 341 Canadian adults surveyed (or followed) from ages 18 to 43. Results showed higher self-esteem at age 18 was associated with more adaptive interactions and lower perceived relationship risk at age 43. A more rapid increase in self-esteem through the transition to adulthood into midlife (ages 18–43) was also associated with more frequent adaptive interactions and less relationship risk at age 43. These results held after accounting for potential confounding variables. This study is the first to demonstrate self-esteem trajectories over a quarter century predict midlife intimate relationship functioning.