During the last few years many different terms for children, adolescents and adults with ADHD have been introduced. They were mainly influenced by American descriptions of the classification system DSM-IV:

• ADHD (Attention-Deficit/Hyperactivity Disorder)
  is the term used in the current Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) diagnostic criteria.
• ADD (Attention Deficit Disorder) with or without hyperactivity
  is the older term from the DSM-IIIR. Thus in some older literature you will find this term as a synonym for ADHD.

Thomas Brown describes common symptoms of ADD (inattentive type):

• Often easily distracted by extraneous stimuli
• Often difficulty following through on instructions from others
• Difficulty sustaining attention
• Often does not seem to listen to what is being said
• Tendency to lose things necessary for tasks or activities
• Difficulty organizing goal-directed activities
• Often shifts from one uncompleted activity to another

Some research shows that children with hyperactive-impulsive symptoms tend to have more behavioural problems and conduct disorder, while children with the inattentive type (ADD) have a higher risk of comorbid depression or anxiety disorders.

Children with several symptoms of both the inattentive and the hyperactive type are diagnosed as "combined type" ADHD.