Objective: Current understanding of executive function deficits in Attention-Deficit/Hyperactivity Disorder (ADHD) is derived almost exclusively from neuropsychological testing conducted in laboratory settings. This study compared children's performance on both neuropsychological and real-life measures of executive function and processing speed. Method: The Stroop and Wisconsin Card Sorting Task (WCST) were selected as neuropsychological measures, whereas route tasks in a videogame and at the zoo were used to index real-life measures. Participants comprised a community sample of 22 unmedicated boys with ADHD individually matched on age and IQ with 22 normally developing control boys. Results: There were no group differences in executive function on the Stroop or zoo tasks, but the ADHD group exhibited deficits in set-shifting as assessed by the WCST (perseverative errors and responses) and videogame play (fewer challenges completed). Also, the ADHD group showed slowed processing speed on the Stroop (slower color naming) and zoo activity (longer time to complete task), as well as a slower rate of acquisition of the sorting rule on the WCST (more trials to complete first category). Efficient and flexible videogame play (number of challenges completed) was related positively to efficacy on the Stroop (number of items named correctly in the interference and two control conditions) and inversely related to set-shifting problems on the WCST (perseverative responses and errors). Also, problems in goal-directed behavior at the zoo (number of deviations from designated route) were related to problems in set-shifting on the WCST (perseverative responding). Conclusions: Children with ADHD exhibit impairments in executive function and processing speed in real-world activities as well as in neuropsychological testing. Cognitive deficits detected by standardized neuropsychological testing are related to performance difficulties in real-world activities. (Contains 1 figure and 2 tables.)