Although increasing STEM achievement and STEM participation are widely held goals, research has yet to examine the relation between STEM course participation and STEM grades at the University level. Math attitudes have been shown to be important for math achievement at the primary, secondary, and post-secondary level, but how math attitudes affect decisions to participate in STEM in University is unexplored as well as the gender differences associated with it. We examined the relations between math attitudes and STEM grades and courses taken while accounting for covariates to answer 3 questions: To what extent does STEM achievement relate to STEM participation? Do the same math attitudes that predict STEM achievement predict STEM participation? Does gender moderate the relation between math attitudes and either STEM achievement or STEM participation?