Children with ADHD often demonstrate sudden and intense shifts in both positive and negative affect. This study examined the role of diagnostic status on emotional impulsivity in children utilizing ecological momentary assessment (EMA). Parents of 64 8–12 year old children (15 ADHD-only; 27 ADHD-comorbid; 22 control) completed a diagnostic structured interview and then an EMA protocol, rating the child’s affect thrice daily for 28 days. Analysis of covariance (ANCOVA) suggested that children with ADHD and a comorbid disorder demonstrated significantly more EMA-derived emotional impulsivity than children with ADHD only and control children. No difference was found between children with ADHD only and control children. This study suggested that children with ADHD demonstrate significantly higher levels of emotional impulsivity than control children only in the presence of a comorbid disorder.