This study assessed social skills in 116 children aged 7-12 with ADHD-Combined Type (ADHD-C; n=33), ADHD-Inattentive Type (ADHD-I; n=45), and comparison children (n=38), with consideration of the role sluggish cognitive tempo (SCT) symptoms play in distinguishing profiles. Social skills were assessed using a novel computerized chat room task, in which participants were encouraged to join a conversation and type messages to interact with four computer-simulated peers. Every participant received the identical stimulus from the simulated peers, but was free to respond to it in his or her own unique way. Relative to comparison children, children with ADHD-C made off-topic and hostile responses; children with ADHD-I made off-topic responses, few responses and showed poor memory for the conversation. ADHD subtype differences remained after statistical control of IQ, reading achievement, typing skill, and comorbid disruptive behavior disorders. SCT symptoms, most prevalent among children with ADHD-I, predicted a distinct pattern of social withdrawal and lower hostility. Parent and teacher ratings and in-vivo observations of social skills correlate with this new measure.