BACKGROUND: Mindfulness-Based Interventions (MBIs) have been increasingly proposed as treatment in patients with Attention-Deficit/Hyperactivity Disorder (ADHD), showing promising results on different proposed outcomes, in both children and adults. OBJECTIVES: To systematically review and meta-analyse studies concerning the effects of MBIs on either ADHD and associated features, associated clinical conditions, neurocognitive impairments, mindfulness skills, global functioning and quality of life. METHODS: Searches were conducted on five databases, including controlled and observational studies on both adults and children populations. The review process was compliant to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA). Meta-analyses and meta-regression models were conducted. RESULTS: Thirty-one full-texts were included. In both adults and children, MBIs showed to be more effective than waiting lists in improving ADHD symptoms and some other outcomes. In adults, a medium pooled effect size was shown by meta-analysis for ADHD symptoms but in some cases a publication bias was detected. Subgroup analysis and meta-regression confirmed the gap detected by our systematic review between the medium/large effect size of inactive-controlled studies and the low/negligible one of active-controlled studies. In children, no active-controlled studies have been conducted. Mindfulness Awareness Practice (MAP) and Mindfulness Based Cognitive Therapy (MBCT) were the most used protocols in adult studies, whereas a combination of MBCT and Mindfulness Based Stress Reduction (MBSR) was more preferred for children and adolescent patients. CONCLUSIONS: Even if further studies with a better methodology are needed, we can suggest the MBIs may be useful as complementation and not as replacement of other active interventions.