Psychotherapeutic agents are often administered without sufficient testing to children and adolescents, often on a long-term basis, to reduce aggression. Many pressures, including managed care, will increase the utilization of pharmacotherapy in the outpatient setting to treat serious problems. Lithium is the most promising agent for the treatment of aggression in children and adolescents. However, it has not been shown that lithium is an effective treatment for these patients in the outpatient (non-hospital) setting, or on a long-term basis. The purpose of this study is to examine the long-term effects of lithium used to treat children and adolescents with aggressive conduct disorder (severe aggression).