Recent findings related to individual and contextual factors leading to violence imply significant interactions between temperamental and contextual factors, such as family adversity.15- 20 Children raised in a family environment characterized by young mothering, nonintact family, and poverty and who display individual risks, such as neuropsychological deficits or difficult temperament, are more at risk of showing conduct disorder symptoms during adolescence.21- 24 These individual-environment interactions appear to trigger a developmental trajectory that has been identified as early-onset persistent type, as opposed to late-onset or adolescent-limited type, which is triggered more generally by contextual factors during adolescence.22,25,26 In a cross-fostering analysis of criminality, Cloninger et al27,28 found that adopted children who had a congenital predisposition (ie, biological parents were criminals) and postnatal predisposition (ie, inadequate parenting practices on the part of their adoptive parents) were more likely to become criminals as adults compared with children who displayed only 1 risk. Raine29 found that 70.2% of all violence in their cohort was committed by children who displayed both family adversity and individual risks. Recently, important studies on the role of reduced autonomic activity and antisocial behavior have been published. These studies19 are closely linked to research on the personality dimensions of psychopathy. This field of research has emphasized the role of hyperactivity, fearlessness, and lack of prosociality as enduring individual differences and temperament markers of future antisocial behavior and social selection of deviant peers.17,30,31 These dimensions of temperament were shown to be highly heritable and relatively stable over time32- 34 and are the basis of more complex higher-order personality traits that appear later in life such as conscientiousness, neuroticism, and agreeableness.34- 37 In many studies,21,33,38,39 high levels of hyperactivity and impulsivity in childhood have been related to conduct problems during adolescence. Because hyperactive children are more likely to be caught in a coercive cycle in their relationship with their parents40 or to be rejected by their peers,41- 43 they may be more prone to use aggression in their relationships. Other studies33,44,45 have found that fearlessness or low levels of anxiety increase the risk of later conduct problems. Finally, antisocial behavior has also been linked to lack of prosociality and helpfulness.17,33,46- 49 Children who are less empathic and helpful tend to be less concerned by distress and the negative effects they have on others.50 Although many studies51,52 have linked a given behavioral dimension, such as hyperactivity, to early conduct problems, some studies30,33,53 suggest that taking 2 or even 3 dimensions into account can increase the predictive power. Past studies have provided some understanding of predictors of deviant peer group membership.11,13,14,54 However, these studies9,14 are of limited value when planning early prevention efforts because they assessed predictive factors at the end of the elementary school years or in middle school, when, in the worst cases, deviant peer group association has been or is about to be initiated.