Attention deficit/hyperactivity disorder (ADHD) is one of the most common and impairing child psychological disorders, frequently encountered in pediatric primary care settings. Such a disorder is not only an obstacle to the child's and to the community's actual well-being, but is also a risk factor for future risk-taking, antisocial behavior and psychopathology. In diagnosing such a disorder, clinicians should take into account the most important DSM-IV diagnostic criterion, ADHD-specific-impairment. Authors discuss the central role of impairment evaluation in defining the presence and severity of ADHD, intervention urgency, planning and evaluation, and, in Italy, the need for drug therapy. A comprehensive evaluation of impairment, including investigations about learning difficulties, internalizing symptoms, and maladjustment in social contexts, as consequences of ADHD primary and secondary symptoms, is suggested. The children's global assessment scale (C-GAS), one of the common scales used in Italy to assess impairment, seems to give too general and vague information. Even if an accurate interview relative to the different aspects of impairment is necessary, the authors propose the use of the impairment rating scale (IRS), as an easy, reliable, and valid instrument that could initially (and finally) qualify and quantify impairment present in the child's life, both in school and nonschool settings.