Objective: Background: Children with velocardiofacial syndrome (VCFS), a contiguous deletion syndrome, have an increased prevalence of attention deficit/hyperactivity disorder (ADHD). Method: The authors compared youth with VCFS+ADHD (from the SUNY Upstate VCFS Research Program) to those with ADHD but not VCFS (from the Massachusetts General Hospital Longitudinal Family Studies of ADHD). Results: Children with VCFS+ADHD were more likely to be diagnosed with the inattentive subtype and differed from idiopathic ADHD in the frequency of several inattentive symptoms that appear linked to general cognitive functioning. After controlling for IQ differences, parents of children with VCFS+ADHD endorsed more thought and social problems on a rating checklist. Patterns of comorbidity also differed between the two groups of children with ADHD: Children with idiopathic ADHD had higher rates of comorbid major depression and disruptive behavior disorders. Conclusion: Children with VCFS+ADHD may have a different profile of ADHD symptoms and comorbidity when compared to children with idiopathic ADHD. (J. of Att. Dis. 2007; 11(1) 64-73)