Children suffering from attention deficit hyperactivity disorder (ADHD) may remit until adulthood. But, more than 60–80 % have persisting ADHD symptoms. ADHD as an early manifesting neurodevelopmental disorder is considered a major risk factor for the development of comorbid psychiatric disorders in later life. Particularly, personality disorders are oftentimes observed in adult patients suffering from ADHD. If ADHD and personality disorders share common etiological mechanisms and/or if ADHD as a severely impairing condition influences psychological functioning and learning and leads to unfavorable learning histories is unclear. The development of inflexible and dysfunctional beliefs on the basis of real and perceived impairments or otherness due to the core symptoms of ADHD is intuitively plausible. Such beliefs are a known cause for the development of personality disorders. But, why some personality disorders are more frequently found in ADHD patients as for example antisocial and borderline personality disorder remains subject of debate. Because of the high prevalence of ADHD and the high impact of personality disorders on daily functioning, it is important to take them into account when treating patients with ADHD. Research on the developmental trajectories leading to personality disorders in adult ADHD patients might open the door for targeted interventions to prevent impairing comorbid clinical pictures.