Previous research has established a link between weight-based teasing and binge eating, though the precise mechanisms that drive this relationship remain unknown. This study examined negative affect as a mediator of the relationship between weight-based teasing and binge eating. Participants included 265 adolescent female twins (aged 10-15 years). Self-report measures assessed binge eating, weight-based teasing, and negative affect. Mediation was tested within hierarchical linear models to control for the non-independence of the twin data. Significant positive associations were observed between binge eating, teasing, and negative affect. In the regression analyses, negative affect partially mediated associations between weight-based teasing and binge eating. Results suggest that increases in negative affect are one way in which weight-based teasing leads to binge eating in girls. Future studies should examine additional mediators and assess possible clinical applications of these findings.