The fields of positive psychology, cognitive behavioral therapy, mindfulness, and goal-setting have all demonstrated that individuals can modify their beliefs, attitudes, intentions, and behaviors to improve their subjective happiness. But which ethical beliefs affect happiness positively? In comparison to ethical belief systems such as deontology, consequentialism, and altruism, rational egoism appears to be alone in suggesting that an individual’s long-term self-interest and subjective happiness is possible, desirable, and moral. Albeit an important theoretical foundation of the rational egoism philosophy, the relationship (...) between rational egoism and subjective happiness has yet to be investigated empirically. Using (Overall and Gedeon, Business and Professional Ethics. 38:43–78, 2018) 24-item rational egoism scale, we test this relationship on a random sample of 534 full-time American workers using partial least squares structural equation modelling (PLS-SEM). Consistent with rational egoism theory, the main contribution to knowledge of this research is finding a statistically significant relationship between rational egoism and subjective happiness. Implications for practice and areas for future study are suggested. (shrink)