A common psychiatric disorder of childhood characterized by attentional difficulties, impulsivity, and hyperactivity; known earlier as attention deficit disorder. A disorder or a syndrome comprises a group of signs and symptoms which tend to cluster together (symptoms refer to what the patient experiences; signs refer to what the physician observes). Other older names for this disorder include minimal brain dysfunction, minimal brain damage, hyperactivity, hyperkinesis, and hyperactive child syndrome. Over time, these names were modified due to their implications about etiology and core symptoms: minimal brain dysfunction seemed to imply that children with this disorder were brain-damaged, while hyperactivity and its synonyms named a feature seen in many but not all of these children. Recent studies indicate that attention deficit hyperactivity disorder tends to follow a chronic course, persisting in many cases not only into adolescence but into adulthood.