ADHD adults (N = 26) were compared to normal controls (N = 26) on 6 neuropsychological measures believed sensitive to frontal lobe–executive functioning. MANOVA analyses and subsequent univariate tests indicated that most of the neuropsychological measures discriminated between the two groups. To address clinical significance, diagnostic classification rates were also generated for each measure individually, and for the battery as a whole. Levels of positive predictive power (PPP) for each of the 6 measures (83–100%) indicated that abnormal scores on these tests were good predictors of ADHD. However, estimates of negative predictive power (NPP) suggested that normal scores poorly predicted the absence of ADHD. When classification rates were calculated for the overall battery classification accuracy improved substantially. Thus, neuropsychological tests can differentiate adults suffering from ADHD from adults without ADHD, while also providing good classification accuracy. Finally, the pattern of neurobehavioral impairments exemplified through the Summary Index scores was interpreted as consistent with conceptualizations of ADHD depicting mild neurologic dysfunction in networks associated with the frontal lobes. (JINS, 1999, 5, 222–233.)