Objective: This study aimed to examine the accuracy of self-reports of children and adolescents with ADHD in evaluating activity limitations. Method: Self-reports of children/adolescents with ADHD (n = 89) were compared with those of nonreferred children (n = 94), relative to parent reports about children’s competence. Competence was measured with a 34-item rating scale. Behavioral disorders were documented with the Child Behavior Checklist. Results: Children/adolescents with ADHD were much more likely than controls to overestimate their competence in certain daily activities relative to parent reports, demonstrating a positive illusory bias. Positive illusory bias was found to be pronounced in activities, which were expected to be affected by symptoms of ADHD. Overestimations of competencies were more likely to be accompanied with externalizing problems. Conclusion: Results support the presence of the positive illusory bias also in the domain of everyday life activities. Improvement of self-evaluation of competencies should become a focus of treatment. (J. of Att. Dis. 2013; XX(X) 1-XX)