Cognitive deficits in working memory (WM) are characteristic features of Attention-Deficit/Hyperactivity Disorder (ADHD) and autism. However, few studies have investigated cognitive deficits using a wide range of cognitive measures. We compared children with ADHD ("n" = 49) and autism ("n" = 33) with a demographically matched control group ("n" = 79) on a multidimensional battery of cognitive ability. Results confirmed previous research that both groups were characterized by deficits in WM. However, results also suggest verbal WM measures were better predictors than nonverbal WM measures. In addition, measures of visual-motor integration are equally discriminating of children with ADHD and autism from a matched control group. In all, 81% discrimination accuracy was obtained using only WM and visual-motor integration measures. Demonstrated shared deficits in WM and visual-motor integration are explained based on proposed neurological mechanisms common across the two disorders. Clinical implications are discussed.