The present study investigated the relation between executive functioning and symptoms of Attention-Deficit/Hyperactivity Disorder (ADHD) and Oppositional Defiant Disorder (ODD) in children aged 4-6. A population-based sample (n = 201) was used and laboratory measures of inhibition, working memory and verbal fluency and teacher ratings of disruptive behaviour problems were collected. Both group differences and linear relations were studied and comorbidity was controlled for dimensionally. In both categorical and dimensional analyses, executive functioning was associated with symptoms of ADHD, but not with symptoms of ODD when controlling for comorbidity, and no significant interactive effects of ADHD and ODD symptoms were found. Effect sizes for significant effects were generally in the medium range. Regarding sex differences, the control for comorbid ODD symptoms appeared to affect the relation between ADHD symptoms and executive functioning somewhat more for girls compared with boys. In conclusion, poor executive functioning in preschool appears to be primarily related to symptoms of ADHD, whereas the relation to symptoms of ODD can be attributed to the large overlap between these two disruptive disorders. (Contains 3 tables.)