Aim: Emerging research indicates that gene mutations within the RAS-MAPK signaling cascade, which cause Noonan syndrome and related disorders, affect neurophysiologic activity in brain regions underlying attention and executive functions. The present study examined whether children with Noonan syndrome are at heightened risk for symptoms of attention-deficit-hyperactivity disorder (ADHD) and executive dysfunction relative to an unaffected sibling comparison group, and investigated three key aspects of behavioral attention: auditory attention, sustained attention, and response inhibition. Method: Children and adolescents with Noonan syndrome (n=32, 17 males, 15 females, mean age 11y 3mo, SD 3y) and their unaffected siblings (n=16, eight males, eight females, mean age 11y, SD 3y 6mo) were administered standardized tests of intellectual functioning and clinic-based measures of behavioral attention. Parent ratings of ADHD symptoms, executive functioning, and behavior were also obtained. Results: Children with Noonan syndrome demonstrated higher rates of past ADHD diagnosis, as well as reduced performance compared with unaffected siblings on behavioral attention measures. Parent-rated functional impairments in attention, social skills, working memory, and self-monitoring were more prevalent in the Noonan syndrome group. The relationship between attention regulation skills (sustained attention and inhibitory control) and intellectual test performance was significantly stronger in the Noonan syndrome group than the comparison group. Interpretation: Clinical screening/evaluation for ADHD and executive dysfunction in Noonan syndrome is recommended to facilitate appropriate intervention and to address functional impact on daily life activities.