Attention deficit hyperactivity disorder is a neurodevelopmental disorder characterised by executive dysfunction occasioning symptoms of inattention, hyperactivity, impulsivity and emotional dysregulation that are excessive and pervasive, impairing in multiple contexts, and otherwise age-inappropriate.

A meta-analysis of 175 research studies worldwide on ADHD prevalence in children aged 18 and under found an overall pooled estimate of 7.2% (Thomas et al. 2015). The US Census Bureau estimates 1,795,734,009 people were aged 5-19 worldwide in 2013. Thus, 7.2% of this total population is 129 million—a rough estimate of the number of children worldwide who have ADHD.

There is no single test to diagnose ADHD, and many other problems, such as sleep disorders, anxiety, depression, and certain types of learning disabilities, can also have symptoms similar to ADHD. The diagnosis can be made by a mental health professional, like a psychologist or psychiatrist, or by a primary care provider, like a pediatrician.

Standard treatments for ADHD in adults typically involve medication, education, skills training and psychological counseling. A combination of these is often the most effective treatment. These treatments can help manage many symptoms of ADHD , but they don't cure it.