We compared verbally matched attention-deficit/hyperactivity disorder (ADHD), Williams syndrome (WS), and typically developing individuals (N = 19 each group) on behavioral symptoms (Conners ADHD rating scale) and neuropsychological functioning. Neuropsychological tasks included those that assessed short-term memory and executive functions from the CANTAB (Cambridge Neuropsychological Test Automated Battery) neuropsychological battery. Children with WS scored within the abnormal range and did not differ in severity from ADHD children on the Conners Oppositionality, Cognitive Problems/Inattention, Hyperactivity, and ADHD Index subscales. The WS and ADHD groups also showed similar patterns of neuropsychological functioning, particularly in working memory (WM) strategy use and delayed short-term memory (STM). The findings may have clinical implications for the management of individuals with WS, highlighting the potential significance of behavioral, educational, and pharmacological strategies and treatments known to be useful in the treatment of children with ADHD for individuals with WS.