Clomipramine is a tricyclic antidepressant that was the first effective agent in the treatment of OCD. Its capacity to block serotonin reuptake appears to be essential to reducing the primary symptoms of OCD. Like other tricyclic agents, CMI has an array of possible side effects including gastrointestinal, autonomic, hepatic, and cardiac problems that need to be considered in the clinical management of children and adolescents treated with CMI. Evaluation of clinical response begins with the identification of target symptoms and monitoring the change in these target symptoms over time. This effort can be aided by the use of clinical rating instruments such as the Children's Yale-Brown Obsessive Compulsive Scales and, to a limited degree, drug plasma levels. Although many OCD patients manifest a positive response to CMI, some patients do not. This variation suggests that other neurochemical systems may be implicated in OCD.