Numerous studies have found significant comorbidity between Attention-Deficit/Hyperactivity Disorder (ADHD) and anxiety disorders in children (e.g., Bauermeister et al., 2007; Busch et al., 2002), but limited research has examined factors that may underlie or explain this relationship (e.g., Lilienfeld, 2003; Baldwin & Dadds, 2008). This study aimed to contribute to the development of a comprehensive understanding of the relationship between symptoms of ADHD and symptoms of anxiety in children. The sample for this study was comprised of a clinical population of 258 boys and girls, ages 12-17. ADHD-related symptomology was measured using the Conners' Parent Rating Scale-Revised (CPRS-R), Conners' Teacher Rating Scale-Revised (CTRS-R), and Conners/Wells' Adolescent Self-Report Scale (CASS). Anxiety symptoms were measured using the Multidimensional Anxiety Scale for Children (MASC). Major results indicated CASS Emotional Problems was the best predictor for the MASC Total; MASC Physical Symptoms Total and MASC Social Anxiety (Humiliation/Rejection) were the best predictors for CASS Emotional Problems; CASS Cognitive Problems/Inattention was significantly correlated with the MASC Total; and gender was not a significant predictor for the MASC Total. The results suggest considerable implications for practice, namely that children were the best reporters for their own internalizing symptomology; clinicians ought to be mindful of the limitations of assessing children based on parent or teacher report alone. The significant positive associations identified may render ADHD and anxiety symptomology difficult to distinguish in children, emphasizing that accurate detection of symptomology is critical for making accurate diagnoses and, consequently, developing more appropriate treatment plans for children with ADHD and/or anxiety. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]