The purpose of this study is to assess changes in ADHD symptoms and tolerability of medication in children and adolescents switching from a stimulant to atomoxetine.

Inclusion Criteria:

• Patients must be at least 6 years of age and not yet be 18 years of age at the completion of visit 6
• Patients must meet DSM-IV diagnostic criteria for ADHD (any subtype)
• Patients must have laboratory results showing no significant abnormalities (significant would include laboratory deviations requiring acute medical intervention or further medical evaluation)
• Patients must be of normal intelligence as assessed by the investigator (that is, without a general impairment of intelligence and likely, in the investigator's judgment, to achieve a score of greater than or equal to 70 on a IQ test)
• Patients must be able to swallow capsules

Exclusion Criteria:

• Patients who weigh less than 22 kg or more than 70 kg at study entry
• Patients who have a history of Bipolar I or Bipolar II Disorder, psychosis, or a pervasive developmental disorder
• Patients with a history of any seizure disorder (other than febrile seizures) or prior EEG abnormalities related to epilepsy, or patients who have taken (or are currently taking) anticonvulsants for seizure control
• Patients with a history of severe allergies to more than one class of medication, or multiple adverse drug reactions
• Patients who have glaucoma