Although several studies have suggested an association between attention deficit hyperactivity disorder (ADHD) and non-suicidal self-injury (NSSI) as well as suicidal attempts (SA), few have considered the confounding impact of a comorbid borderline personality disorder (BPD). In the present study, we conducted a retrospective analysis on 147 ADHD patients to assess the role played by BPD in the association between ADHD and lifetime history/number of NSSI and SA. BPD was considered both categorically and dimensionally. Overall, ADHD symptoms were positively associated with a higher lifetime history/number of NSSI and SA. This association was maintained after further adjustment on comorbid BPD status, but not after adjustment on BPD symptoms. While being only exploratory, these results add evidence on the complex links between ADHD and NSSI/SA and suggest a potential role played by BPD symptoms in this association.