<b><i>Introduction:</i></b> Growing, albeit heterogenous evidence questions whether attention deficit/hyperactivity disorder (ADHD) is associated with socio-cognitive impairments, especially beyond childhood. This study focuses on mentalizing – the socio-cognitive ability to attribute and reason in terms of mental states. We aimed to characterize mentalizing performance in terms of correct scores and types of errors in adolescents and young adults with ADHD. <b><i>Methods:</i></b> Forty-nine adolescents and adults with ADHD and 49 healthy controls matched for age and gender completed a computerized naturalistic mentalizing task, the Movie for Assessment of Social Cognition (MASC). Repeated measures analyses of variance examined the effects of age group and ADHD diagnosis on MASC performance. Additionally, associations between mentalizing scores, the severity of attention problems, and the presence of comorbidity were explored in the ADHD group. <b><i>Results:</i></b> Results showed an increased prevalence of hypomentalizing errors in adolescents with ADHD. Lower mentalizing scores in adolescents with ADHD were correlated with indices of inattentiveness, impulsivity, and vigilance problems. Hypomentalizing errors in adolescents showed to be particularly associated with inattentiveness, after controlling for age and comorbidity. In contrast, adults with ADHD performed similarly to controls and their scores on the mentalizing task were not correlated to attention problems. <b><i>Conclusion:</i></b> These findings highlight potential developmental differences in mentalizing abilities in ADHD youths and their association with attentional impairments.