Objective: Very few studies have investigated intervention approaches that may be efficacious for youth with ADHD and co-occurring cognitive disengagement syndrome (CDS) symptoms. This study examined the feasibility, acceptability, and preliminary efficacy of a mindfulness-based intervention for adolescents with ADHD and co-occurring CDS symptoms. Methods: Fourteen adolescents ages 13 to 17 years (35.71% female; 64.29% White, 7.14% Black, 28.57% Multiracial) with ADHD and elevated CDS symptoms completed the 8-week group-based Mindful Awareness Practices (MAPs) program developed for individuals with ADHD. We collected measures of CDS, ADHD, mind-wandering, mindfulness, and other difficulties and functioning at baseline, 1-month post-intervention, and 3-month post-intervention to examine preliminary efficacy. We measured participant session attendance, session engagement, at-home practice adherence, and satisfaction of adolescents and caregivers at 1-month post-intervention to examine feasibility and acceptability. We also collected qualitative feedback from adolescents and caregivers at 1-month post-intervention. Results: The intervention was overall feasible to administer, and caregivers and adolescents reported satisfaction with the intervention despite some difficulties with attendance and engagement. We observed improvements to both caregiver- and adolescent-reported CDS symptoms and ADHD-inattentive symptoms from pre-intervention to post-intervention time points, though findings across 1- and 3-month follow-up differed based on informant. We also observed improvements to some indices of adolescent-reported mind-wandering, mindfulness, brooding rumination, and academic functioning. For caregiver report, the only other noted improvement was for executive functioning. No improvements were reported by teachers. Conclusions: Findings support the initial feasibility, acceptability, and preliminary efficacy of MAPs for adolescents with ADHD and co-occurring CDS symptoms on a range of outcomes. Larger trials with a randomized design are warranted to further examine mindfulness-based interventions for adolescents with ADHD and co-occurring CDS symptoms.