In the previous two chapters we examined sex differences in the early risk predictors for antisocial behaviour. We continue this theme in this chapter by turning our attention to sex differences in the relation between personality and antisocial behaviour. A personality analysis of sex differences in antisocial behaviour may improve our understanding of the diathesis underlying antisocial disorders. Personality research has already described the nature of the propensity toward antisocial behaviour by organizing information about the individual differences in cognitions, motivations, emotions, and distinct styles of approach and response to the world that robustly predict criminal offending (Moffitt et al., 1995). Just as males and females differ on their antisocial involvement on average (chapters 3 and 4), males and females are also known to differ on their personalities on average (Feingold, 1994). If population sex differences in personality traits could account for the sex difference in antisocial behaviour this conjunction would suggest that measured quantitative personality traits may be a window on to core diatheses underlying antisocial disorders. Such a window could deepen our understanding of antisocial propensity because findings about the origins of personality traits are rapidly emerging from several quarters in the behavioural sciences. Longitudinal studies attest to developmental links from early childhood temperament to later adult personality (Caspi, 2000; Caspi et al., forthcoming).