In this study, the authors aimed to examine 4 domains of executive functioning in adults with attention-deficit/hyperactivity disorder (ADHD)-namely interference control, concept shifting, verbal fluency, and verbal working memory. Four groups of participants were included: (a) adults diagnosed with ADHD (ADHD(-): n = 20), (b) adults diagnosed with both ADHD and 1 or more comorbid disorder(s) (ADHD(+): n = 22), (c) adults referred for ADHD because of ADHD symptomatology but not diagnosed as such (non-ADHD; n = 34), and (d) healthy controls (n = 136). ADHD-related deficits (independent of comorbidity) were revealed for concept shifting and verbal working memory. In addition. the ADHD(+) and non-ADHD groups displayed deficits in terms of general processing speed. Given that these deficits were not found in the ADHD(-) group, the authors contend that these deficits are likely attributable to comorbidity rather than ADHD itself. Contrary to the authors' expectations, these findings do not correspond with the cognitive subtype hypothesis.