Background Adherence to attention deficit hyperactivity disorder (ADHD) medication can prevent serious consequences, possibly with lifelong effects. Numerous factors have been observed that influence adherent behaviour, but the impact of personality traits has been inadequately explored. The purpose of this study was to explore the associations between personality traits and adherence to ADHD medication, beliefs about the medication, and perceptions of ADHD. Method Adolescents (n = 99) on ADHD medication were administered: Health-Relevant Personality Traits Five-Factor Inventory, Medication Adherence Report Scale, Beliefs about Medicines Specific and Brief Illness Perceptions Questionnaires. Results The personality trait Antagonism correlated with adherence behaviour (r = - 0.198, p = 0.005) and perceived personal control of ADHD (r = - 0.269, p = 0.007). Negative Affectivity correlated with beliefs regarding necessity (r = 0.319, p = 0.001), concerns (r = 0.344, p = 0.001), and experienced side effects of medication (r = 0.495, p = 0.001), alongside perceptions regarding duration (r = 0.272, p = 0.007), identity (r = 0.388, p < 0.001), being emotionally affected (r = 0.374, p < 0.01), personal control (r = - 0.287, p = 0.004) and concerns about ADHD (r = 0.465, p < 0.001). Impulsivity correlated with perceived consequences (r = - 0.226, p = 0.0255) and personal control of ADHD (r = - 0.379, p < 0.001). Hedonic Capacity correlated with concerns about medication (r = - 0.218, p = 0.0316) and perceived identification with ADHD (r = - 0.203, p = 0.045). Conclusion Personality traits are related to adherence, beliefs about ADHD medicines and perceptions of ADHD. Antagonism is associated with adherence, especially intentional non-adherence, while Negative Affectivity correlates with numerous perceptions of ADHD and beliefs about medications. Personality assessments could be useful in the care and treatment of adolescents with ADHD.