Nonsuicidal self-injury (NSSI) and eating disorder behaviours (EDB) may share a similar emotion dysregulation mechanism. This study examined the relations between repeated rumination episodes and emotions in NSSI and EDB within the context of the Emotional Cascades Model (Selby, Anestis, & Joiner, 2008), which suggests that ruminating on negative events increases the intensity of negative emotion; negative emotion prompts continued rumination, which further increases the intensity of the negative emotion. Individuals with a history of NSSI and/or EDB reported higher levels of negative emotions and lower levels of positive emotions, relative to individuals without a history of these behaviours. Similarly, a history of NSSI was associated with greater initial increases in negative emotions, and a history of EDB was associated with greater initial decreases in positive emotions, following rumination. While these results support the presence of emotion dysregulation in NSSI and EDBs, it only partially supports the emotional cascades model. / CIHR graduate award helped to fund this research.