Gender-based inequalities in health have been frequently documented. This paper examines the extent to which these inequalities reflect the different social experiences and conditions of men's and women's lives. We address four specific questions. Are there gender differences in mental and physical health? What is the relative importance of the structural, behavioural and psychosocial determinants of health? Are the gender differences in health attributable to the differing structural (socio-economic, age, social support, family arrangement) context in which women and men live, and to their differential exposure to lifestyle (smoking, drinking, exercise, diet) and psychosocial (critical life events, stress, psychological resources) factors? Are gender differences in health also attributable to gender differences in vulnerability to these structural, behavioural and psychosocial determinants of health? Multivariate analyses of Canadian National Population Health Survey data show gender differences in health (measured by self-rated health, functional health, chronic illness and distress). Social structural and psychosocial determinants of health are generally more important for women and behavioural determinants are generally more important for men. Gender differences in exposure to these forces contribute to inequalities in health between men and women, however, statistically significant inequalities remain after controlling for exposure. Gender-based health inequalities are further explained by differential vulnerabilities to social forces between men and women. Our findings suggest the value of models that include a wide range of health and health-determinant variables, and affirm the importance of looking more closely at gender differences in health.