Although Attention Deficit Hyperactivity Disorder (ADHD) is well established as a diagnosis in childhood, the diagnosis in adults remains controversial. The present study compared the Continuous Performance Test (CPT) performance of 60 clinic-referred adults with current ADHD symptomatology to normal subjects. Adults with current ADHD symptoms were found to make more errors of omission and commission than did normal adults. The signal detection theory variable, d', indicated that patients with ADHD were less sensitive to stimulus features than were normals. Using several CPT measures to predict group status, the CPT appeared to be of moderate clinical utility. These CPT results lend convergent validity to similar results in child populations and help to establish ADHD as a valid disorder of adulthood.