Disruptive and antisocial behavior in youth is the longest and most heavily studied syndrome in child and adolescent mental disorders. This interest is understandable as externalizing behaviors are more alarming and easily noticed by caregivers, resulting in the disruptive behavior disorders being the most frequent referral problem for youth and accounting for one-third to half of all cases seen in mental health clinics. This focus also reflects the recognition that adult sociopathy is almost always preceded by disruptive behavior in childhood, and our current understanding of antisocial behavior development is the most detailed description of the course of any psychopathology over the life span. The study of and intervention efforts with antisocial youth had a direct impact on the development of child mental health care in the United States. The founding of juvenile court clinics in 1899 to deal with delinquents directly resulted in the creation of the child guidance movement and the establishment of child and adolescent psychiatry as a subspecialty.