Objective: To assess personality traits using the Temperament and Character Inventory (TCI) in a group of 63 previously diagnosed ADHD patients and 68 population controls and investigate the impact of common comorbid psychiatric disorders on these personality measures. Method: Psychiatric comorbidity was assessed with the Mini International Neuropsychiatric Interview Plus and personality traits by the TCI. Results: The patient group had significantly higher scores on the TCI dimensions Harm avoidance and Novelty seeking compared with the control group. However, when adjusting for comorbid anxiety and depressive disorder, the ADHD group no longer showed higher Harm avoidance than the control group. The difference in Novelty seeking between the patient and control groups was correlated with lifetime diagnosis of antisocial personality disorder (ASPD). Conclusion: It is important to take comorbid psychiatric disorders into account while investigating personality traits in ADHD.