2. 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 that, in the opinion of the examining clinician, will contraindicate treatment with LDX or confound efficacy or safety assessments. Comorbid psychiatric diagnoses will be established at the Screening Visit (Visit -1)of the antecedent study (SPD489-325)with the Screening interview of the Kiddie-SADS-Present and Lifetime-Diagnostic Interview (K-SADS-PL)and additional modules if warranted by the results of the initial interview. Participation in behavioural therapy is permitted provided the subject was receiving the therapy for at least 1 month at the time of the Baseline Visit (Visit 0) of the antecedent study (SPD489-325).