There must be clear evidence of significant problems in social, academic or occupational functioning. 

Some of the symptoms were present before age 7. 

Some impairment from the symptoms is present in two or more settings, such as home or work. 

The symptoms aren't better accounted for by another mental disorder (mood or anxiety disorder).

 And, either exhibits six or more of the following symptoms of inattention for at least six months.

    Often fails to give close attention to details or makes careless mistakes.
    Often has difficulty sustaining attention.
    Often does not seem to listen when spoken to directly.
    Often does not follow through on instructions and fails to finish schoolwork, chores or work duties.
    Often has difficulty organizing tasks and activities.
    Often avoids tasks that require sustained mental effort.
    Often loses important things.
    Often is easily distracted.
    Often is forgetful.
 

Or, exhibits six or more of the following symptoms of hyperactivity or impulsivity for at least six months:

      Often fidgets or squirms in seat.
      Often leaves seat inappropriately.
      Often feels restless.
      Often has difficulty playing or engaging in leisure activities quietly.
      Often act as if "driven by a motor."
      Often talks excessively.
      Often blurts out answers before questions have been completed.
      Often has difficulty awaiting turn.
      Often butts into conversations or intrudes on others.