The objective of this study is to identification of neuropsychological, genetic and neuroimaging markers and treatment response predictors of attention-deficit/hyperactivity disorder (ADHD). Participants who take the standardized pharmacotherapy (methylphenidate or atomoxetine) for ADHD will be observed for 52 weeks. They will do several neuropsychological, neuroimaging and genetic tests at visit 1~6.

Inclusion Criteria:

1. aged between 6 and 12 years
2. met the Diagnostic and Statistical Manual IV Text Revision (DSM-IV-TR) diagnostic criteria for ADHD and needed pharmacotherapy.
3. Informed consent

Exclusion Criteria:

1. presence of intellectual disability or learning disorder

2. past and/or current history of bipolar disorder or psychosis or substance use disorder

3. past and/or current history of pervasive developmental disorder, organic mental disorder or other neurological disorder

4. presence of sever suicidal ideation

5. presence of tic disorder or obsessive-compulsive disorder whose symptoms needed pharmacotherapy

6. presence of family history with Tourette's Syndrome

7. took medication with methylphenidate or atomoxetine with last 6 month (or more than 3 month)

8. presence of severe medical condition (ex. cardiologic, liver, kidney, pulmonary, glaucoma)

9. took alpha 2 adrenergic receptor agonist, antidepressant, antipsychotics, benzodiazepine, modafinil, antiepileptic drug or dietary supplement that have a influence on Central Nervous System (CNS).

10. presence of possibility with pregnancy

11. especially for neuroimaging,

    1. uncooperative with claustrophobia or body movement
    2. metal material inside body that can't take off

Total 600 children and adolescents will be enrolled in this study. 500 patients in psychiatric outpatient will be enrolled. 100 persons of healthy volunteers will be recruited via advertisements.