This study examines the utility of a variety of neuropsychological measures of attention in the assessment of Attention-Deficit/Hyperactivity Disorder (ADHD) in adults. The Attentional Impairment Index (Al) is introduced along with a procedure for computation, and is intended as an experimental measure which can be used to indicate the presence and severity of an attentional problem. Results indicated that the severity of attentional impairment (Al) was affected by the number of diagnoses, subtype of ADHD, and group classification (No Diagnosis, ADHD, or Other Psychiatric diagnoses). Overall group differences indicate a decline in performance on the neuropsychological test measures as the severity of diagnosis increased, with two exceptions. One was the number of failures to maintain response set on the WCST, and the other was the overall level of attentional impairment as measured by the Al Index. Both of these scores were most impaired in the ADHD group. The summary measures from the Stroop, WCST, FSIQ, and Trail Making Test successfully differentiated both the clinical groups from those not meeting full diagnostic criteria for any disorder. ecent media coverage on the topic of ADHD iñ~ adults has considerably increased the number of elf-referred individuals for diagnosis and treatment of ADHD. Since 1972, when ADHD was first recognized in adults as Adult Brain Dysfunction (Mann & Greenspan, 1972), its acceptance as a valid diagnosis for adults has increased. Longitudinal, retrospective, and family studies indicate that this disorder often continues into adolescence and adulthood for a large proportion of affected individuals (