The co-occurrence of attention-deficit hyperactivity disorder (ADHD) and substance use disorders has received considerable attention in recent clinical and scientific investigations. These two disorders are linked to one another in a variety of ways. The core symptoms of ADHD may be mimicked by the effects of psychoactive substance use, making it difficult to diagnose one disorder in the presence of the other. Individuals with ADHD may demonstrate earlier onset of the substance abuse and a pattern of more frequent or intense use. ADHD symptoms were explored as possible antecedents of opioid dependence. A total of 109 adult opioid-dependent, treatment-seeking male and female outpatients were investigated with an extended clinical semistructured interview to collect sociodemographic, drug-related, and clinical data. The results indicate that ADHD alone does not predispose the development of opioid dependence in our sample. Childhood ADHD symptoms may nevertheless be found more frequently related to school performance problems and difficulties in social adaptation, which was identified in more than half of our population. Patients with ADHD history seemed to experience a drug abuse career with more complications which need to be recognized with focused attention in order to start earlier treatment strategies.