This will be an open label study using daily does of up to 126mg/day of Concerta in the treatment of children and adolescents, ages 12-17, who meet DSM-IV criteria for ADHD. Specific hypotheses are as follows:

Hypothesis 1: Children and adolescents with ADHD will have significantly higher ACC and DLPFC Glutamate/myo-Inositol containing compounds (Glu/Ino) and Glutamate/creatine + phosphocreatine (Glu/Cr) than matched HCS.

Hypothesis 2: After six weeks of treatment, OROS methylphenidate will lower ACC and DLPFC Glu/Ino and Glu/Cr levels in children with ADHD who are methylphenidate responders.

The primary objective of this study is to use 1H MRS to assess Glutamate (Glu), myo-Inositol (Ino), and creatine + phosphocreatine (Cr) levels in brain regions of interest in 20 children with ADHD between the ages of 12-17 years old, before and after a six-week open treatment trial with OROS methylphenidate. For comparison, 1H MRS will also be obtained from 20 controls matched by age and gender. We also will scan 20 children with ADHD between the ages of 12-17 years old that are currently enrolled in the protocol entitled "Prevention of Cigarette Smoking in ADHD Youth with Concerta" (2003-P-001313) and on a stable dose of Concerta. These 20 children will be scanned once while on medication and once while off medication

Inclusion Criteria:

1. Male or female subjects, 12-17 years of age.
2. ADHD subjects must meet study criteria for the "Prevention of Cigarette Smoking in ADHD Youth with CONCERTA Protocol"; #2003-P-001313.
3. Control subjects must not meet full DSM-IV criteria for Attention Deficit Hyperactivity Disorder, or any other current major psychiatric disorder.
4. Each subject and his/her authorized legal representative must understand the nature of this proposed study, and must sign informed consent and informed assent documents.
5. Subject and parent must have a level of understanding sufficient to communicate intelligently with the investigator and study coordinator, and to cooperate with study procedures.

Exclusion Criteria:

1. Clinically significant chronic medical condition including hepatic, renal, gastroenterologic, respiratory, cardiovascular (including ischemic heart disease), endocrinologic, neurologic, immunologic, or hematologic disease.
2. Organic brain disorders or mental retardation (I.Q. <75).
3. Contraindication to MRI including presence of metal or surgical devices (plates, implants, braces or other items).
4. Pregnancy; women of child bearing potential must be using a medically approved method of birth control. Women of child bearing potential will receive a urinary pregnancy test prior to each MR scanning session.
5. Severe phobia of being in small, enclosed spaces.
6. Investigator and his/her immediate family; defined as the investigator's spouse, parent, child, grandparent, or grandchild will not be eligible to participate in the treatment arm of the study.