This study examined relationships among self-esteem, media internalization, sexual orientation, and ethnicity in predicting drive for muscularity in a diverse group of men (N = 217) who work out in gyms. Investigations examined media internalization and sexual orientation as moderators of the relationship between self-esteem and drive for muscularity. Additional analyses examined media internalization as a moderator of the relationships between a) sexual orientation and drive for muscularity and b) ethnicity and drive for muscularity. Standardized questionnaires were utilized to assess drive for muscularity, media internalization, self-esteem, sexual orientation, and ethnicity. While lower self-esteem predicted greater drive for muscularity, neither media internalization nor sexual orientation were significant moderators of this relationship. However, media internalization mediated the relationships between sexual orientation and drive for muscularity and between ethnicity and drive for muscularity. Findings suggest that the internalization of ideal muscularized images explain demographic differences in the drive to be more muscular.