Although years from publication, committees creating the next edition of the Diagnostic and Statistical Manual of Mental Disorders (5th edition, DSM–V) will begin meeting next year to consider many potential changes to diagnostic criteria, including those for ADHD. High on most lists for modification for ADHD are likely to be the separation of the inattentive subtype from the other subtypes (e.g., Milich, Balentine, & Lynam, 2001) and a liberalizing of the age–of–onset criterion (e.g., Barkley & Biederman, 1997; McGough & Barkley, 2004). Another domain which, in our view, warrants reconsideration is Criterion D, which requires “clear evidence of clinically significant impairment in social, academic, or occupational functioning” that has an early onset and is present in two or more settings. (American Psychiatric Association, 2000, p. 93). Unlike criteria related to symptoms, DSM–IV has little to say about what constitutes impairment. It offers no operational definition, no strategies for how impairment should be measured, any guidance on the extent of impairment necessary to be “clinically significant,” any stipulations as to the essential domains of impairment that should be included or excluded in diagnosis, or how one determines whether impairment is caused by ADHD–type symptoms or other phenomena (e.g., borderline intellectual functioning). The lack of specificity or detail with regard to impairment in the DSM–IV warrants serious attention in the next edition. The DSM–IV is much clearer on the types and numbers of symptoms necessary to make a diagnosis of ADHD. This level of specificity has not been applied to the impairment criterion, yet it is