OBJECTIVE: The aim of the present study was to evaluate the relationship of probable attention-deficit hyperactivity disorder (ADHD) with novelty seeking (NS), the severity of psychopathology and borderline personality disorder (BPD) in a sample of male patients with opioid use disorder (OUD). METHODS: Participants included 229 patients with OUD. Participants were evaluated with the Adult ADHD Self-Report Scale (ASRS-v1.1), the Symptom Checklist-90-Revised (SCL-90-R) and NS subscale of the Temperament and Character Inventory (TCI). In addition, BPD was assessed with the Structured Clinical Interview for DSM-III-R-Personality Disorders (SCID-II). RESULTS: Age, duration of education, marital and employment status did not differ between those with probable ADHD (n = 54, 23.1%) and those without (n = 175, 76.9%). The severity of psychopathology, NS and subdimensions (other than NS1, which was lower) were higher among those with the probable ADHD. ADHD scores were midly correlated with NS scores, other than NS1. In logistic regression analyses, the severity of NS, particularly Impulsiveness (NS2), together with general psychopathology, predicted probable ADHD, whereas the presence of BPD had no effect. CONCLUSIONS: These findings suggest that trait impulsivity, together with the severity of psychopathology, is related with the probable ADHD, while the presence of BPD has no effect among adult patients with OUD.