Clonidine is a central acting a2-agonist used primarily as an antihypertensive agent. Recently, it has been used for the treatment of attention deficit hyperactivity disorder in children and adolescents. When taken in excess, it can produce profound CNS depression, apnea, bradycardia and hypotension. A transient period of hypertension can sometimes occur. Treatment is primarily supportive, including respiratory support, atropine for bradycardia, and fluids and dopamine for hypotension. The CNS depression sometimes responds to naloxone. Young children are very sensitive to the toxic effects of clonidine. A case of an 11 year old adolescent who took an overdose of his clonidine is described to illustrate the toxicity of this agent.