The diagnostic criteria for attention-deficit hyperactivity disorder (ADHD) require both symptoms and impairment to be present. Impairment in functioning is commonly the primary reason for referral, and is also a better predictor of long-term outcomes than ADHD symptoms. And yet, only recently has research begun to examine the impact of ADHD treatments on functional impairment using efficient and psychometrically sound outcome measures. In this article, we identify several noteworthy multidimensional measures of functional impairment (ADHD FX, Barkley Functional Impairment Scale [BFIS], Impairment Rating Scale [IRS], Weiss Functional Impairment Rating Scale [WFIRS]) utilized in recent clinical trials for ADHD, and describe their psychometric properties and clinical utility. We also review existing evidence on the impact of pharmacological and behavioral treatments on different domains of functional impairment in ADHD youth as measured by these specific measures. Further research is needed to evaluate longitudinal effects of ADHD treatments on functional impairment, and the use of these measures in adaptive treatment designs.