Attention deficit hyperactivity disorder (ADHD) is a prevalent neurobehavioral disorder that affects individuals in early childhood and is characterized by cognitive impairments associated with executive functioning. However, the exact nature of the impairment(s) is/are unclear. In a recent meta-analysis, Miyake, Friedman, Emerson, Witzki, Howerter, and Wager (2000) demonstrated that there are at least three separable frontal executive functions: set switching, working memory updating, and response inhibition. Here we used event-related potentials (ERPs) to investigate whether the cognitive impairments seen in ADHD are specific to one of these executive functions or rather represent a global executive functioning deficiency. The current studies examined the time course and scalp localization of executive functions in Combined Type ADHD and in comparison control children by implementing modified versions of three executive tasks used by Miyake et al. (2000), local-global, tone-monitoring, and Stroop; versions more appropriate for the ADHD population. An additional non-executive task (visual oddball) was included in order to demonstrate that the deficits in ADHD are specific to executive functioning. The goal was to determine if children with ADHD perform differently on these three executive tasks and if this difference can be attributed to a deficit associated with one or more of the executive functions. The current findings show that ADHD impacts only a subset of cognitive operations in the executive functions, leaving the other ERPs in the executive tasks and the visual oddball unaffected. Specifically, the ADHD group was impaired on tasks involving allocation of attention and response inhibition, the cognitive operations most closely related to the diagnostic criteria for this subtype of ADHD. These findings may extend our knowledge of the time course and localization of executive functions and provide a tool for studying the nature of disrupted executive functioning in ADHD.