Inclusion Criteria:

• Diagnosis of ADHD according to the Diagnostic and Statistical Manual of Mental Diseases, Fourth Edition (DSM-IV), obtained via interview with an adapted version of the K-SADS E module for ADHD
• Described chronic course of ADHD symptomatology from childhood to adulthood, with some symptoms present before age 7 years, which continue to meet DSM-IV criteria at the time of assessment. ADHD is not diagnosed if the symptoms are better accounted for by another psychiatric disorder [e.g. mood disorder (especially bipolar disorder), anxiety disorder, psychotic disorder, personality disorder]
• CGI-Severity baseline score ≥ 4 (at least "moderate" severity)
• Female patients must be postmenopausal for at least one year, surgically sterile, or practicing an effective method of birth control (e.g., prescription oral contraceptives, contraceptive injections, intrauterine device, double-barrier method, contraceptive patch, male partner sterilization) before entry and throughout the study
• Have a negative urine pregnancy test at baseline
• Patients must have signed an informed consent form indicating that they understood the purpose of and procedures required for the study and are willing to participate in the study
• Patient agrees to take only the supplied study drug as treatment for ADHD during the study
• Patient is able to comply with the study visit schedule and willing and able to complete the protocol-specified assessments

Exclusion Criteria:

• Known allergy or hypersensitivity to methylphenidate, or components of CONCERTA®
• Known to be a non-responder to methylphenidate in adequate doses (i.e., 0.8 - 1.0 mg/Kg)
• Has been treated with any methylphenidate or amphetamine containing medication within 4 weeks of the screening visit
• Hamilton's Depression Scale, suicide item higher than 2
• Any psychiatric condition including the following, but not limited to: acute mood disorder, schizophrenia, bipolar disorder I, obsessive compulsive disorder (OCD), anti-social personality disorder
• Subjects with Autism or Asperger's syndrome
• Subjects with a history of Tourette's syndrome
• A diagnosis of substance use disorder (abuse/dependence) according to DSM-IV criteria within 6 months prior to screening evaluation (nicotine and caffeine dependence are not exclusionary). Episodic abuse in the past is not an exclusion criterion
• Known or suspected mental retardation
• Hyperthyroidism, myocardial infarction or stroke in the 6 months prior to the screening visit
• Patients with history of seizures (ongoing seizure disorder), glaucoma or uncontrolled hypertension
• Patients with any co-existing medical condition or who are taking any concomitant medication that is likely to interfere with safe administration of methylphenidate including any herbal or homeopathic remedies
• Herbal and over-the-counter weight loss or diet preparations or drugs that contain stimulants
• Use of monoamine oxidase inhibitors, except if tapering off, within 4 weeks of the baseline visit
• Use of selective-serotonin reuptake inhibitors and tricyclic antidepressants
• Use of other psychotropic medications used to treat comorbidities (not ADHD) if dose of the medication has not remained stable for a minimum of 4 weeks prior to trial entry
• Subjects who have clinically significant gastrointestinal problems (small bowel inflammatory disease, "short gut" syndrome due to adhesions or decreased transit time, past history, peritonitis, cystic fibrosis, chronic intestinal pseudo-absorption or Meckel's diverticulum), including severe narrowing (pathologic or iatrogenic) of the gastrointestinal tract
• Serious or unstable illnesses including, but not limited to liver or renal insufficiency, significant cardiac, vascular, pulmonary, gastrointestinal, endocrine, neurological, psychiatric or metabolic disturbances
• Have received an experimental drug or used an experimental medical device within 30 days before the planned start of treatment
• Female patient who is pregnant or breastfeeding