Open-Label, Chronic Exposure, Safety Study of CLONICEL (Clonidine HCl Sustained Release) in Children and Adolescents With Attention Deficit Hyperactivity Disorder (ADHD)

Inclusion Criteria: * Male or female subject who has completed either study CLON-301 or study CLON-302, or discontinued early for reasons other than adverse events necessitating discontinuation * Age between 6 and 17 years, inclusive * Diagnosis of attention deficit hyperactivity disorder of the hyperactive or combined inattentive/hyperactive subtypes according to Diagnostic and Statistical Manual of Mental Disorders IV (DSM IV) criteria * General good health as judged by the Principal Investigator * Body mass index (BMI) ≥ 5th percentile of the subject's age group according to the CDC growth chart. BMI is calculated using the formula: weight (kg) / \[height (m)\]2 * 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 intrauterine device * 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 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 * Presence of a disorder that would interfere with the absorption, metabolism, or excretion of clonidine * Presence of alcohol or drug abuse.