Essential facts Attention deficit hyperactivity disorder (ADHD) is a condition characterised by inattentiveness, hyperactivity and impulsivity, according to the ADHD Foundation. Most young people with a sustained diagnosis will go on to have significant difficulties in adulthood, which may include continued ADHD, personality disorders, emotional and social difficulties, substance misuse, unemployment and involvement in crime (NICE 2008). Some people tend to be mainly hyperactive and impulsive, while others are principally inattentive. Symptoms of ADHD are distributed throughout the population and vary in severity. Only those with significant impairment meet criteria for a diagnosis of ADHD. Research suggests it affects about 5% of children.