Objective: Current recommendations for evaluation and diagnosis of attention-deficit hyperactivity disorder (ADHD) are meant for primary care settings and may not adequately address the needs of children seen in subspecialty developmental-behavioral pediatric settings who may have higher rates of comorbid developmental, learning, and psychiatric disorders. The authors sought to characterize the diagnostic complexity of school-aged children diagnosed with ADHD after comprehensive multidisciplinary evaluation in a subspecialty developmental-behavioral pediatric clinic., Methods: The authors conducted a retrospective medical record review of 144 patients aged 7 to 11 years who were consecutively evaluated by an interdisciplinary team (developmental-behavioral pediatrician, psychologist, educator) in a school-age clinic within a developmental-behavioral pediatrics tertiary care center from January 1, 2009 to December 31, 2009., Results: After comprehensive evaluation, rates of ADHD diagnosis increased from 32.6% (n = 47) preevaluation to 54.2% (n = 78) postevaluation (p < .0001). Rates of learning disorders among children receiving a final diagnosis of ADHD increased from 2.6% (n = 2) preevaluation to 50% (n = 39) postevaluation. (p < .0001). Among children receiving a final diagnosis of ADHD, 73.1% (n = 57) were diagnosed with at least 1 comorbid psychiatric, developmental, or learning disorder., Conclusions: Among school-aged children diagnosed with ADHD in a developmental-behavioral pediatric subspecialty setting, a comprehensive evaluation including developmental, neuropsychological, and educational assessments yielded high rates of comorbid psychiatric, developmental, and learning disorders. This supports the need to provide comprehensive interdisciplinary assessment for such children to ensure the identification and treatment of not only the core symptoms of ADHD but also the comorbidities that may otherwise go unrecognized and therefore not optimally treated.