Background: Antisocial behaviour may partly develop as a consequence of psychopathic personality. However, neither the direction of effects nor the aetiology of the association has previously been clarified. The aim in this study was to investigate the direction of effects between psychopathic personality and antisocial behaviour, and to investigate the genetic and environmental contribution to this association. Method: Twins (n = 2,255) in the Swedish Twin Study of Child and Adolescent Development were prospectively followed from adolescence to adulthood. We used a longitudinal cross-lagged twin model to study the associations between psychopathic personality and antisocial behaviour. Results: Psychopathic personality in mid-adolescence predicted antisocial behaviour in adulthood (p less than 0.001), but not the other way around. However, bidirectional effects were found when a measure of persistent antisocial behaviour (from age 8-9 to age 16-17) was used. Psychopathic personality predicted both rule-breaking behaviour (p less than 0.001) and aggressive behaviour (p less than 0.01). Genetic factors were of importance in mediating the longitudinal associations between psychopathic personality and antisocial behaviour. Conclusions: This study provides evidence that genetically influenced psychopathic personality is a robust predictor of adult antisocial behaviour, but also that persistent antisocial behaviour has an impact on adult psychopathic personality via genetic effects.