Attention Deficit Hyperactivity Disorder (ADHD) is highly prevalent among adults with addictive disorders, but little is known about addiction patterns associated with ADHD diagnosis. This study examined addiction severity in patients with co-occurring addictive disorders and ADHD controlling for the potential influence of associated psychiatric comorbidity. Data were collected in French outpatient addiction treatment centers. A total of 217 patients seeking treatment for substance or gambling addiction were included. At treatment entry, participants were interviewed with the Addiction Severity Index, the Conners Adult ADHD Diagnosis Interview for the DSM-IV (CAADID), the Mini International Neuropsychiatric Interview (MINI) and the Structured Clinical Interview for DSM-IV Axis II for borderline personality disorder (SCID II). History of ADHD was associated with an earlier onset of addiction, poly-dependence (defined by presence of at least two current substance dependence diagnoses in addition to tobacco dependence if present) and borderline personality disorder. Persistence of ADHD during adulthood was associated with a higher prevalence of poly -dependence. This study highlights the need for early implementation of preventive interventions for substance use or behavioral addiction in children/adolescents with ADHD and the need to consider ADHD in the treatment of addictive disorders.