Empathy has been accepted as a crucial factor in the development of prosocial thought and behavior. This study attempted to clarify the role of empathy in the development of antisocial and aggressive delinquent behavior. The subjects were 331 delinquents and 64 nondelinquent controls ages 12 to 18. The delinquents were found to be significantly delayed or arrested in the development of empathy. The nondelinquent group exhibited a significant age-related increase in empathy during the adolescent period, whereas the delinquent group did not. Of three delinquent subgroups utilized, the neurotics were least empathic, the psychopathics next, and the subculturals the most empathic; the groups differed significantly from each other. Aggressive delinquents were significantly lower in empathy level than nonaggressive delinquents, though differentiation by type of aggression (person or property) was not significant.