Disorder, attention deficit (ADD): Often referred to as attention deficit hyperactivity disorder (ADD or ADHD), a disorder that is characterized by hyperactivity or restlessness, trouble concentrating, and/or trouble controlling one's impulses. It is one of the most common conditions of childhood and adolescence. Most experts agree that this condition affects 8%-10% of school-age children and that more than 40% of children with ADHD grow up into adults with this disorder. Rather than having any single cause, attention deficit hyperactivity disorder(ADHD) develops from both genetic and life experience risk factors. Individuals with ADHD tend to have problems developing efficient self-regulation skills and decision-making abilities. Biologically, ADHD is a neurochemical and neuroanatomical disorder.