The purpose of this study is to evaluate the safety and tolerability of atomoxetine alone versus atomoxetine plus low-dose, sustained-release MPH in children with treatment-resistant ADHD.

Inclusion Criteria:

• Patients will be at least 6 years of age and not more than 12 years of age at visit 1
• Patients must meet DSM-IV diagnostic criteria for ADHD
• Patients must be retrospectively identified as stimulant non-responders
• 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 an IQ test)
• Patients must be able to swallow capsules

Exclusion Criteria:

• Patients who weigh less than 22 kg or more than 60 kg at study entry
• Patients who have a history of Bipolar I or Bipolar II Disorder, psychosis, or pervasive developmental disorder
• Patients who meet DSM-IV criteria for anxiety disorder or autism
• Patients with a history of any seizure disorder and/or Rolandic seizures (other than febrile seizures) or prior electroencephalogram (ECG) abnormalities in the absence of seizures, 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, including hypersensitivity to MPH