The official definitions of ADHD are as follows:
* According to the U.S. Surgeon General, and ICD-9-CM (International Classification of Disease Revised Edition 2005), ADHD is a neurological deficit classified as "metabolic encephalopathy" affecting the release and homeostasis of neurological chemicals and the functioning of the limbic system.
* The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders-IV (Text Revision) (DSM-IV-TR) gives three subtypes of ADHD:
o Predominantly Inattentive,
o Predominantly Hyperactive-Impulsive, and
o Combined Type.
Although most diagnoses of ADHD are made for children, the DSM definition of ADHD does not confine the disorder solely to childhood. In fact, many adults are also diagnosed. Current theory holds that approximately 30% of children diagnosed retain the disorder as adults. Although the disorder may not have been diagnosed in an individual during childhood, it is also currently thought that all adults with Adult attention-deficit disorder (AADD) had it in childhood. Hyperactivity and other symptoms may be less noticeable in adults with ADD/ADHD who have learned better coping skills and other forms of adaptive behavior than they had as children. Particularly in adults, studies have shown a high correlation between ADHD and creativity. Many painters and performing artists seem to show significant evidence of ADHD, particularly those drawn to improvisational humor and stand up comedy (see Robin Williams, the poster child for adult ADHD). ADHD can lead to underachievement among some people when not given the right support and attention.