Objective: This study investigated the role of sluggish cognitive tempo (SCT) in relation to externalizing and internalizing mental health problems, academic functioning, and social functioning among young adolescents with attention-deficit/hyperactivity disorder (ADHD). Method: In all, 57 youth ages 10 to 14 participated in the study. Parents rated SCT, internalizing, and externalizing symptoms, as well as social and academic impairment. Teachers rated academic and peer impairment, and intelligence and academic achievement also were assessed. Results: Above and beyond ADHD and conduct problem symptoms, SCT was associated with internalizing mental health symptoms and social problems. The association between SCT and externalizing problems or academic functioning was not significant when accounting for ADHD symptomatology and intelligence. Conclusion: SCT is consistently associated with internalizing symptoms and is also associated with young adolescents’ general social difficulties. When controlling for important related constructs, SCT is not associated with externalizing symptoms or academic impairment among young adolescents with ADHD. (J. of Att. Dis. 2011; XX(X) 1-XX)