Body image dissatisfaction is a significant risk factor in the onset of eating pathology and depression. Therefore, understanding predictors of negative body image is an important focus of investigation. This research sought to examine the contributions of body mass, appearance conversations with friends, peer appearance criticism and internalization of appearance ideals to body dissatisfaction among adolescents. The sample was comprised of 239 (54% female) adolescents, with a mean age of 16 years. Self-report questionnaires were completed on body dissatisfaction, peer appearance conversations and criticism, internalization of appearance ideals, height and weight. For girls and boys, body mass, appearance conversations with friends, peer appearance criticism and internalized appearance ideals emerged as significant predictors of body dissatisfaction. Gender moderated the effect of body mass on body dissatisfaction. Internalization mediated the relationship between peer appearance conversations and criticism, and body dissatisfaction. These findings suggest that while body mass exerts a differential risk for body dissatisfaction among boys and girls, internalisation may represent a key psychological process that underpins body dissatisfaction among both boys and girls.