This study investigated the role of externalizing behavior as a mediator of the relation between social self-control and peer liking among children with attention-deficit/hyperactivity disorder-combined type (ADHD-CT). A model was proposed whereby externalizing behavior would fully statistically account for the direct relation of social self-control to peer liking. One hundred seventy-two children ages 7.0–9.9 years with ADHD-CT were rated by their teachers regarding their social self-control and by their parents and teachers regarding their rates of externalizing behavior. Same-sex classmates provided ratings of overall liking. Structural equation modeling was used to assess the proposed model. Results supported the proposed model of externalizing behavior as fully statistically accounting for the relation of social self-control to peer liking. This study demonstrated the crucial role that externalizing behaviors play in the social impairment commonly seen among children with ADHD-CT.