This article reports a comparison on childhood risk factors of males and females exhibitingchildhood-onset and adolescent-onset antisocial behavior, using data from the Dunedinlongitudinal study. Childhood-onset delinquents had childhoods of inadequate parenting,neurocognitive problems, and temperament and behavior problems, whereas adolescent-onsetdelinquents did not have these pathological backgrounds. Sex comparisons showed amale-to-female ratio of 10:1 for childhood-onset delinquency but a sex ratio of only 1.5:1 foradolescence-onset delinquency. Showing the same pattern as males, childhood-onset females hadhigh-risk backgrounds but adolescent-onset females did not. These findings are consistent withcore predictions from the taxonomic theory of life-course persistent and adolescence-limitedantisocial behavior.