The Wechsler Intelligence Scale for Children-Fourth Edition General Abilities Index and Cognitive Proficiency Index have been advanced as possible diagnostic markers of attention deficit hyperactivity disorder. This hypothesis was tested with a hospital sample with attention deficit hyperactivity disorder (n = 78), a referred but nondiagnosed hospital sample (n = 66), a school sample with attention deficit hyperactivity disorder (n = 196), a school matched comparison sample (n = 196), and a simulated standardization sample (n = 2,200). On the basis of receiver operating characteristic analyses, the General Abilities Index-Cognitive Proficiency Index discrepancy method had an area under the curve of (a) 0.64, 95% CI [0.58, 0.71] for the hospital attention deficit hyperactivity disorder sample compared with the simulated normative sample, (b) 0.46, 95% CI [0.37, 0.56] for the hospital attention deficit hyperactivity disorder sample compared with the referred but nondiagnosed hospital sample, (c) 0.63, 95% CI [0.59, 0.67] for the school attention deficit hyperactivity disorder sample compared with the simulated sample, and (d) 0.50, 95% CI [0.45, 0.56] for the school attention deficit hyperactivity disorder sample compared with the matched comparison sample. These area-under-the-curve values indicate that the General Abilities Index-Cognitive Proficiency Index discrepancy method has low accuracy in identifying children with attention deficit hyperactivity disorder. (Contains 6 figures and 2 tables.)