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. 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. 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. 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.