BACKGROUND: In the last three decades, there has been increased interest in studying the association between religion/spirituality (R/S), and mental health and functional outcomes. METHODS: Using data from a contemporary, nationally representative sample of 3151 U.S. military veterans maintained by GfK Knowledge Networks, Inc., we evaluated the relation between R/S and a broad range of mental health, and psychosocial variables. Veterans were grouped into three groups based on scores on the Duke University Religion Index: High R/S (weighted 11.6%), Moderate R/S (79.7%) and Low R/S (8.7%). RESULTS: A "dose-response" protective association between R/S groups and several mental health outcomes was revealed, even after adjustment for sociodemographic and military variables. High R/S was associated with decreased risk for lifetime posttraumatic stress disorder (odds ratio [OR]=0.46), major depressive disorder (MDD; OR=0.50), and alcohol use disorder (OR=0.66), while Moderate R/S was associated with decreased risk for lifetime MDD (OR=0.66), current suicidal ideation (OR=0.63), and alcohol use disorder (OR=0.76). Higher levels of R/S were also strongly linked with increased dispositional gratitude, purpose in life, and posttraumatic growth. LIMITATIONS: In this cross-sectional study, no conclusions regarding causality can be made. The study provides a current snapshot of the link between R/S and mental health. The study also cannot determine whether religious coping styles (negative vs positive coping) contributed to observed differences. CONCLUSIONS: Although the present study does not have treatment implications, our results suggest that higher levels of R/S may help buffer risk for certain mental disorders and promote protective psychosocial characteristics in U.S. military veterans.