 Attention deficit hyperactivity disorder, ADHD, is a common neurodevelopmentally disorder affecting approximately 5% of school-aged children worldwide. In this meta-analysis, we found that the prevalence of ADHD in children and adolescents is estimated at 7.6% for ages 3 to 12 and 5.6% for ages 12 to 18, respectively. These results are significantly higher than those reported previously, suggesting that the prevalence of ADHD may be increasing over time. This article was offered by Nader Salari, Homan Kasimi, Nasreen Abdelay, and others.