This study examined the moderating effects of different aspects of trait impulsivity on trajectories of negative affect prior to and following body checking in the natural environment in women with anorexia nervosa (AN). Body checking is a compulsive behavior that may maintain the cycle of eating disordered behavior through negative reinforcement. Previous studies regarding the relationship of negative affect to body checking have been inconsistent, making it unclear how negative affect functions as an antecedent to this behavior in the natural environment. We hypothesized that individual differences in trait impulsivity may influence body checking in response to negative affect. Negative urgency (NU) (the tendency to act rashly under distress) and (lack of) perseverance (the tendency to give up on goal directed behavior) may be unique facets of impulsivity that play a role in body checking. Women with AN (n = 82) completed a self-report measure of impulsivity and used ecological momentary assessment (EMA) to record negative affect and body checking for two weeks. Results indicated that women with low (lack of) perseverance experienced a greater increase in negative affect than those with high (lack of) perseverance prior to and following body checking. Overall, results indicate that individual differences in trait impulsivity moderated the relationship of negative affect to body checking in women with AN.