Attention-deficit/hyperactivity disorder (ADHD) is defined in DSM-IV-TR (American Psychiatric Association 2000) as a behavioral disorder of childhood onset (by the age of 7 years) characterized by symptoms of inattentiveness and impulsivity/hyperactivity. Based on the type of symptoms that predominate, DSM-IV-TR recognizes a combined type in which both inattention and hyperactivity/impulsivity symptoms are present, a predominantly inattentive subtype, and a predominantly hyperactive/impulsive subtype. In addition, DSM-IV-TR also recognizes the category of ADHD not otherwise specified (NOS) for individuals presenting with atypical features.