Inclusion Criteria:

• Male or female between 6 and 17 years of age, inclusive
• Diagnosis of ADHD of the hyperactive or combined inattentive/hyperactive subtypes according to DSM-IV criteria
• Minimum score of 26 on the ADHDRS-IV questionnaire at Baseline
• General good health as judged by the Principal Investigator
• Body mass index ≥ 5th percentile of the subject's age group according to the CDC growth chart.
• Ability to swallow tablets
• General IQ ≥80 as judged by the Principal Investigator
• Subject as well as parent/guardian able to sign informed assent or consent form.

Exclusion Criteria:

• If female of child-bearing potential, pregnant or lactating or does not agree to use a medically acceptable form of birth control, such as hormonal medication, double-barrier method, or IUD
• Presence of a clinically significant illness or abnormality on physical examination or clinical laboratory evaluations that, in the opinion of the investigator, would increase the safety risks from clonidine administration or interfere with the ability of the patient to take part in the study.
• Presence of clinically significant abnormality on centrally interpreted Electrocardiogram (ECG) readings
• History or presence of a concomitant psychiatric disorder requiring psychotropic medication or a severe concomitant Axis I or Axis II disorder that could interfere with study assessments in the judgment of the Principal Investigator
• History of concomitant conduct disorder (CD)
• History of seizures, except for a single episode of febrile seizure prior to age 2
• History of syncopal episodes
• Presence of a disorder that would interfere with the absorption, metabolism, or excretion of clonidine
• History of intolerance to clonidine, including any dermatologic reaction to transdermal clonidine
• Presence or history of alcohol or drug abuse
• Positive drug screen, with the exception of ADHD drugs
• Use of any investigational drug within 30 days of study start.