Childhood conduct disorder casts a long shadow over adulthood, often leading to antisocial personality, drug misuse, increased rates of psychosis and earlier death. This article reviews a range of effective treatments, and shows what is ineffective. The common theme underlying interventions that work is that they change the environment around the young person, with parent training emerging as the most effective. Medication is largely ineffective. The task now is to enable more of these interventions to be available at a reasonably early age.