Bulimia nervosa and non-suicidal self-injury (NSSI) co-occur at high rates, and both have been conceptualized as maladaptive emotion regulation strategies. Treatments focusing on emotion regulation have been designed for both problem behaviors, yet, there exists very little research examining the temporal emotional states surrounding acts of NSSI. Using ecological momentary assessment (EMA) methodology, the current study examined the temporal association between positive and negative emotional states prior to and consequent to acts of NSSI within a subset of bulimia nervosa patients. Results indicate significant increases in negative affect, and decreases in positive affect, prior to an NSSI act. Post-NSSI, positive affect significantly increased while negative affect remained unchanged. The findings offer partial support for an emotion regulation paradigm to understanding NSSI within bulimic populations and implications for treatment are discussed.