This study examined the relation between cognitive deficits and positive bias in a sample of 272 children with and without Attention Deficit Hyperactivity Disorder (ADHD; 7-12 years old). Results indicated that children with ADHD with and without biased self-perceptions exhibit differences in specific cognitive deficits (executive processes, working memory, broad attention, and cognitive fluency) compared to each other and to control children. Further, specific cognitive deficits emerged as partial mediators of the relation between ADHD diagnostic status and positive bias. Interestingly, some differences in results emerged based on the domain considered (academic, social, behavioral competence). Results lend initial support to the role of cognitive deficits in the positive bias of some children with ADHD. Implications for future research and intervention are discussed.