While research has shown that the prevalence of ADHD in the general population has increased over time, there have been no studies focused on ADHD prevalence in patients with borderline personality disorder (BPD). This study compares two cohorts of adults with rigorously diagnosed BPD recruited nearly three decades apart (1992 vs. 2020). Participants from the 1992 McLean Study of Adult Development (MSAD) (N = 290) and the 2020 Flourishing study (N = 147) were assessed for ADHD using DSM-III-R…