Background: Research has consistently reported gender differences in mental health, but studies on differences in psychological well-being between women and men have not yielded conclusive results. The aim of this study was to examine the relevance of gender to the psychological well-being of adult individuals. A cross-sectional study with a sample of 1700 men and 1700 women from the general Spanish population was conducted. Their ages ranged from 21 to 64 years, and they were assessed with Ryff’s Psychological Well-Being Scales and the Bem Sex Role Inventory. Results: Men scored higher than women in self-acceptance and autonomy, and women scored higher than men in personal growth and positive relations with others. The most relevant variable in the psychological well-being of both women and men was high masculinity. Other relevant variables in women’s well-being were high femininity, not having a manual occupation, not being homemakers, and professional occupation. Men´s well-being also was higher in professional men and in men with a skilled non-manual occupation, men with high femininity and men who were not single, divorced or widowed. Conclusions: Adherence to traditional gender roles is relevant to the psychological well-being of women and men, and women and men whose self-concept includes both masculine-instrumental and feminine-expressive characteristics have greater well-being.