Understanding the determinants of subjective or self-rated health (SRH) is of central importance because SRH is a significant correlate of actual health as well as mortality. A large body of research has examined the correlates, antecedents, or presumed determinants of SRH, usually measured at a given time or endpoint. In the present study, we investigate whether individual mastery, a prominent indicator of agency, has a positive effect on SRH over a broad span of the life course. Drawing on longitudinal data from the Youth Development Study (n=741), we examine the impacts of mastery on SRH over a 24-year period (from ages 21-22 to 45-46). The findings of a fixed effects analysis, controlling time-varying educational attainment, unemployment, age, obesity, serious health diagnoses, and time-constant individual differences, lead us to conclude that mastery is a stable predictor of SRH from early adulthood to mid-life. This study provides evidence that psychological resources influence individuals' subjective assessment of their health, even when objective physical health variables and socioeconomic indicators are taken into account.