Understanding the mechanisms through which internalisation of societal body standards lead to negative outcomes for women is important to inform prevention and treatment strategies targeting female body image issues and problematic eating and exercise behaviours. This study investigated the mediating roles of body surveillance and social comparison on the relationship between fit-ideal internalisation and a range of negative eating and body image related outcomes. Participants were 448 females, aged 16–25 years who completed self-report measures of fit-ideal internalisation, body surveillance, social comparison, body dissatisfaction, dieting, bulimic behaviours and compulsive exercise. Consistent with hypotheses, the results of parallel mediation analyses suggested that both body surveillance and social comparison mediated the relationship between fit-ideal internalisation and body dissatisfaction, dieting and bulimic behaviours. However, only social comparison was found to mediate the relationship between fit-ideal internalisation and compulsive exercise. The results suggest both body surveillance and social comparison are mechanisms by which fit internalisation detriments women's body image, making them potentially useful treatment targets for future research.