Juvenile Delinquency and Mental Health – In today’s world of rapidly-rising crime, we are compelled to expand our knowledge about crime through an increased understanding of its beginnings in juvenile delinquency. The decade of 1990 saw more youth transferred to criminal court, longer sentences, and lower minimum ages at which juveniles could be prosecuted in the criminal justice system as if they were adults. This increase in juvenile delinquent acts has been accompanied by large increases in both the rate of juvenile drug use and the rate of admission to residential treatment centers for emotionally disturbed children. These temporally-correlated phenomena raise important questions about their possible interrelationship and subsequent effect on the nature of today’s juvenile delinquent. As awareness of the high prevalence of mental health problems among juvenile offenders has grown, researchers and practitioners have recognized the need for reliable and efficient methods of assessing such problems among large numbers of offenders to ensure that limited treatment resources are applied to those with the greatest need. The primary aim of this chapter is to present an overview of studies throughout the world determining the prevalence and types of mental health disorders among youth in the juvenile system in order to gain some understanding of the extent of psychological maladjustment in this population.