A recently validated trait personality framework is the HEXACO (honesty-humility, emotionality, extraversion, agreeableness, conscientiousness, and openness to experience). Little is yet known about how the HEXACO personality dimensions and its subsets--particularly the dimension of honesty-humility--relates to physical activity and body size dissatisfaction as a function of gender. This study tests these relations across men and women through a proposed path model wherein personality and physical activity relate indirectly through lower body size dissatisfaction and perceived fitness in 315 university students. Results pertaining to honesty-humility revealed that women were higher in honesty-humility, emotionality, and conscientiousness. Women with higher honesty-humility (notably sincerity) were prone to lower body size dissatisfaction whereas lower levels of modesty predicted physical activity levels in men. The proposed path model had an excellent fit in both men and women although significant pathways were more prevalent in women than in men. The role of body size dissatisfaction seems to be more salient in explaining the relationship between the HEXACO personality dimensions and perceived fitness and physical activity in women than men. We recommend that practitioners particularly note the vulnerability of women university students who are high in emotionality and low in honesty-humility (especially sincerity) and agreeableness.