Lisdexamfetamine Dimesylate 2-year Safety Study in Children and Adolescents With Attention-Deficit/Hyperactivity Disorder (ADHD)

Inclusion Criteria: For subjects who participated in another SPD489 study (SPD489-317, SPD489-325, or SPD489 326): * Subject is a male or female aged 6-17 years. * Subject participated in SPD489-317, completed 9 weeks of treatment, and completed the 1 week post-treatment safety follow-up visit. For subjects who have not participated in another SPD489 study: * Subject is a male or female aged 6-17 years. * Subject must meet DSM-IV-TR criteria for a primary diagnosis of ADHD based on a detailed psychiatric evaluation. For all subjects: * Subject has a Baseline ADHD-RS-IV total score greater than or equal to 28. * Subject, who is female of childbearing potential (FOCP), must have a negative serum beta Human Chorionic Gonadotropin (HCG) pregnancy test, and a negative urine pregnancy test at Baseline, be non-lactating and agree to comply with any applicable contraceptive requirements of the protocol. * Subject and parent/LAR are willing and able to comply with all the testing and requirements defined, including oversight of morning dosing. Specifically, the parent/LAR must be available upon awakening, at approximately 7:00 AM, to dispense the dose of Investigational Product for the duration of the study. * Subject aged greater than or equal to 18 years has a systolic blood pressure less than or equal to 139 mmHg and a diastolic blood pressure less than or equal to 89 mmHg. * Subject is able to swallow a capsule. Exclusion Criteria: For subjects who participated in another SPD489 study (SPD489-317, SPD489-325, or SPD489 326): * Subject was terminated from a previous SPD489 study (SPD489-325 or SPD489 326) for protocol non-adherence and/or subject non-compliance and/or experienced a medication-related SAE or AE resulting in termination from the previous study. * Subject experienced any clinically significant AEs in a prior SPD489 study (SPD489 317, SPD489-325, or SPD489-326) that, in the opinion of the Investigator, would preclude further exposure to SPD489. For all subjects: * Subject's symptoms are well-controlled on their currently prescribed ADHD medication with acceptable tolerability. * Subject has a positive urine drug result at Screening. * Subject has a current, controlled (requiring a restricted medication) or uncontrolled, comorbid psychiatric diagnosis with significant symptoms such as any severe comorbid Axis II disorder or severe Axis I disorder (such as Post Traumatic Stress Disorder, psychosis, bipolar illness, pervasive developmental disorder, severe obsessive compulsive disorder, severe depressive or severe anxiety disorder) or other symptomatic manifestations, such as agitated states, marked anxiety, or tension. * Subject has taken another Investigational Product or taken part in a clinical study with the exception of a prior SPD489 study (SPD489-317, SPD489 325, or SPD489 326) within 30 days prior to Screening. * Subject weighs less than 22.7 kg (50 lbs). * Subject is significantly overweight. * Subject has a conduct disorder. Oppositional defiant disorder is not exclusionary. * Subject has a concurrent chronic or acute illness (such as severe allergic rhinitis or an infectious process requiring antibiotics), disability, or other condition that might confound the results of safety assessments conducted in the study or that might increase risk to the subject. * Subject is currently considered a suicide risk in the opinion of the Investigator, has previously made a suicide attempt, or has a prior history of, or is currently demonstrating active suicidal ideation. Subjects with intermittent passive suicidal ideation are not necessarily excluded based on the assessment of the Investigator * Subject has glaucoma. * Subject has current abnormal thyroid function, defined as abnormal thyroid stimulating hormone (TSH) and thyroxine (T4). Treatment with a stable dose of thyroid medication for at least 3 months is permitted. * Subject has any clinically significant ECG abnormality. * Subject has any clinically significant laboratory abnormalities. * Subject has a documented allergy, hypersensitivity, or intolerance to any active ingredient or excipients in SPD489. * Subject has a recent history (within the past 6 months) of suspected substance abuse or dependence disorder (excluding nicotine) in accordance with DSM-IV-TR criteria. * Subject has a history of seizures (other than infantile febrile seizures), a chronic or current tic disorder, a current diagnosis of Tourette's Disorder, or a known family history of Tourette's Disorder. Subject has a history of tics that is judged by the Investigator to be exclusionary. * Subject has a known history of symptomatic cardiovascular or cerebrovascular disease, advanced arteriosclerosis, structural cardiac abnormality, cardiomyopathy, serious heart rhythm abnormalities, coronary artery disease, or other serious cardiac problems that may place them at increased vulnerability to the sympathomimetic effects of a stimulant drug. * Subject has a known family history of sudden cardiac death or ventricular arrhythmia. * Subject has a medical condition, other than ADHD, that requires treatment with medications that have central nervous system effects and/or affect performance. Stable use of anticholinergic or theophylline bronchodilators is not exclusionary.