This research applied self-determination theory to examine the degree to which satisfaction of basic psychological needs for autonomy, relatedness, and competence explained the association between socioeconomic status and physical and mental health outcomes, while controlling for age, exercise, and smoking status. This was a survey research study with 513 full-time employees in professions representative of a hierarchal organization. The results of the structural equation model verify that psychological need satisfaction mediates the inverse association between socioeconomic status and physical and mental health. Self-determination theory contributes to understanding the psychosocial roots of the uneven distribution of health across the socioeconomic gradient.