Why are sex differences in internalizing mental health disorders such as depression and externalizing health behaviors such as alcohol problems frequently documented? Despite these reported differences between men and women, what accounts for the wide variation in these health outcomes within sex? Theories of gender role orientation have provided explanations for these gaps, but empirical support is mixed. In this dissertation, I propose an alternative model where the sex-linked personality traits from the BIS/BAS systems inform sex differences and intra-sex variation in two contrasting health outcomes: depressive symptoms and alcohol use problems. I analyze the potential mediating and moderating effects of the BIS/BAS on the relationships between stress and health outcomes in a sample of 1,713 young adults in Miami-Dade County, Florida. Elevated BIS traits among women account for 20 percent of the sex gap in depressive symptoms and exacerbate the effects some social stressors on depressive symptoms. BIS/BAS do not inform sex differences in alcohol use problems, however elements of the BAS traits strongly predict the alcohol behaviors of both sexes, while BIS traits moderate the stress-alcohol relationship among women in contrasting ways. Additionally, the BIS/BAS traits do not operate consistently when considered within race/ethnicity. The results provide a window into the role that individual variation in personalities can contribute to the understanding of important intra-sex and inter-sex variation in the stress process.