Adult attention deficit hyperactivity disorder (ADHD) is often associated with personality pathology. However, only few studies have been conducted on the link between ADHD and pathological narcissism (PN), with or without a diagnosis of narcissistic personality disorder (NPD). In order to fill this gap, PN and NPD were assessed in 164 subjects suffering from ADHD, with several other measures including ADHD severity, quality of life, depression, anxiety, impulsivity, and emotion dysregulation (ED). We found that a significant proportion of ADHD patients suffered from NPD, and that both narcissistic grandiosity and vulnerability were associated with ADHD hyperactivity and impulsivity symptoms, but not with inattentive symptoms. These two dimensions seemed to be negatively associated with well-being and positively associated with most of the other studied psychiatric dimensions except ED, the latter being only associated with vulnerability, even after adjustment on borderline symptoms. Overall, despite important limitations that limit the generalizability of our findings to the overall ADHD population (notably linked to selection bias), we believe that this exploratory study sheds light on the potential clinical relevance of narcissistic pathology in adult ADHD patients.