Very little evidence exists on working memory (WM) deficits in children with disruptive behavior disorders such as Oppositional Defiant Disorder (ODD) or Conduct Disorder (CD). We evaluated the function of visuospatial WM in patients (n = 26) with ODD/CD compared with age- and gender-matched controls (n = 26) while controlling for the comorbid diagnosis of Attention-Deficit/Hyperactivity-Disorder (ADHD) in patients. The patients were diagnosed by Kiddie-SADS-PL interview, psychiatric symptoms were measured using Child Behavior Checklist and Teacher Report Form. WM was measured by computer-based visuospatial n-back tasks with three difficulty levels. Incorrect responses (reflecting WM performance) in all WM tasks were significantly higher in patients with ODD/CD than in controls. Both patient subgroups, ODD/CD + ADHD and ODD/CD alone, had WM deficits compared with controls. These results suggest that children with ODD/CD have visuospatial WM deficits that are not accounted for by comorbid ADHD.