A meta-analysis examined the relationship between psychosocial factors and the development of breast cancer. Average effect sizes (Hedges's g) were calculated from 46 studies for 8 major construct categories: anxiety/depression, childhood family environment, conflict-avoidant personality, denial/repression coping, anger expression, extraversion-introversion, stressful life events, and separation/loss. Significant effect sizes were found for denial/repression coping (g = .38), separation/loss experiences (g = .29), and stressful life events (g = .25). Although conflict-avoidant personality style was also significant (g = .19), the effect size was less robust, and a moderate number of future studies with null results would reduce the significance. Results overall support only a modest association between specific psychosocial factors and breast cancer and are contrary to the conventional wisdom that personality and stress influence the development of breast cancer.