The aim of the current study was to examine the moderating effect of emotion regulation on treatment efficacy following a parent-training intervention, parent-child interaction therapy, for young children born preterm. In this pilot randomized controlled trial, 28 young children who were born preterm (i.e., <37 weeks gestation) and presented with elevated levels of externalizing behavior problems were randomly assigned to an immediate treatment or waitlist control group. Observers masked to treatment condition coded an index of emotion regulation (i.e., global regulation) during a videotaped 10-min parent-child interaction at the initial baseline assessment. Treatment efficacy was assessed using a parent-report questionnaire of child disruptive behavior. Results demonstrated that global regulation significantly interacted with treatment condition in predicting change in child disruptive behavior. Specifically, higher levels of distress at baseline were associated with greater improvements in child disruptive behavior following the intervention. These findings are discussed in the context of the differential susceptibility hypothesis and highlight the importance of considering children's emotion regulation skills in the course of psychosocial treatment for young children born premature.