This study assessed two relevant aspects of executive dysfunction in children with either Tourette syndrome (TS) or ADHD. Process variables derived from existing neuropsychological measures were used to clarify the executive function construct. Clustering of responses on measures of verbal fluency, figural fluency, and verbal learning was examined to assess strategic response organization. Rule breaks, intrusions, and repetition errors were recorded to assess inhibition errors. No significant differences were found among the three groups (TS, ADHD, and controls) on tasks of response organization (clustering). In our sample, both the ADHD and the TS groups were largely free from executive function impairment, and their performance on the fluency and list learning tasks was in the average range. There was a significant group difference on one of the disinhibition variables, with both TS and ADHD groups showing significantly more intrusions on verbal list learning trials than controls. When more traditional total score variables were analyzed among the three groups, there were no significant differences; however, analysis of effect size revealed medium-to-large effect sizes for Letter Word Fluency total score differences (ADHD vs. controls), and for Semantic Word Fluency total score differences (ADHD vs. TS), with the ADHD group having weaker performance in both comparisons. Results provide some support for the use and analysis of process variables—particularly those related to inhibition and intrusion errors, in addition to the total score variables when assessing executive function deficits in children with ADHD and TS. While group differences may be found, children with uncomplicated TS should not routinely be considered to have significant executive function impairments, and when deficits are found, they may be attributable to other comorbid disorders. (JINS, 2001, 7, 102–111.)