Attention-Deficit/Hyperactivity Disorder (AD/HD) is a condition that can make it hard for a person to sit still, control behavior, and pay attention. These difficulties usually begin before the person is 7 years old. However, these behaviors may not be noticed until the child is older.

Doctors do not know just what causes AD/HD. However, researchers who study the brain are coming closer to understanding what may cause AD/HD. They believe that some people with AD/HD do not have enough of certain chemicals (called neurotransmitters) in their brain. These chemicals help the brain control behavior.

There are three main signs, or symptoms, of AD/HD. These are: