We investigated two factors that predict students' achievement and behaviour in undergraduate mathematics: gender and personality. We found that gender predicted students' achievement and behaviour when considered in isolation, but ceased to be predictive when personality profiles were taken into account. Furthermore, personality accounted for significantly more variance in undergraduates' achievement and behaviour than did gender, but the converse was not the case. We therefore argue that personality provides the more productive lens through which to understand the behaviour of undergraduate mathematics students. We relate this finding to recent research emphasising gender differences in mathematics education, and suggest that researchers wishing to promote equity in participation at and beyond the undergraduate level should consider shifting their focus to individual differences in personality.