Individuals with Attention-Deficit Hyperactivity Disorder (ADHD) consistently exhibit a stronger preference for immediate rewards than for larger rewards available following a delay on tasks measuring choice impulsivity (CI). Despite this, however, there remains a dearth of studies examining the impact of stimulant treatment on CI as well as associated higher order (e.g., working memory [WM]) and perceptual (e.g., time perception) cognitive processes. The present study examines the effect of osmotic release oral system methylphenidate (OROS-MPH) on CI, WM and time perception processes as well as the relation among these processes before and after taking a regimen of OROS-MPH. Thirty-five children (aged 7-12 years) with a diagnosis of ADHD participating in a concurrent stimulant medication study were recruited to complete computerized assessments of CI, WM, and time perception. Children completed the assessments after administration of a placebo as well as their lowest effective dose of OROS-MPH following a 2-week titration period. The results from one-sample t-tests indicated that OROS-MPH improves both CI and WM in youth with ADHD but does not impact time perception. Further, results revealed no significant association among the various indices of cognitive performance while taking placebo or OROS-MPH. Overall, the findings suggest that while OROS-MPH improves both CI and WM in youth with ADHD, improvements in CI as a result of OROS-MPH are unlikely to be associated with the improvements in WM given the lack of association among the two. Future studies should consider alternate cognitive, emotional, and motivational mechanisms that may account for the impact of OROS-MPH on CI. (PsycInfo Database Record (c) 2022 APA, all rights reserved).