Two hypotheses--high self-esteem leads children to act on antisocial cognitions (disposition-activating hypothesis) and high self-esteem leads children to rationalize antisocial conduct (disposition-rationalizing hypothesis)--were investigated in two longitudinal studies. In Study 1 (N = 189; mean age = 11.1 years), antisocial behavior was aggression; in Study 2 (N = 407; mean age = 10.8 years) it was avoidance of the mother. In both studies, there was little evidence for the disposition-activating hypothesis but considerable support for the disposition-rationalizing hypothesis. Over time, aggressive children with high self-esteem increasingly valued the rewards that aggression offers and belittled their victims, and avoidant children with high self-esteem increasingly viewed their mother as harassing and uninvolved. For antisocial children, high self-esteem carries costs.