Part of the Cambridge Study in Delinquent Development, a prospective longitudinal survey of 411 males, the aim in this study was to devise scales at different ages (10, 14, 18, and 32) that were the best measures available of the definitions of conduct disorder, antisocial personality disorder, and psychopathy included in this project. Significant continuity was evident in antisocial personality from childhood to adulthood, but the proportion of antisocial children who become antisocial adults depends crucially on what cut-off points are used. Generally, about half of the most antisocial males at an earlier age were among the most antisocial at a later age. Similarly, about half of the most antisocial males at a later age had been among the most antisocial at an earlier age. The weakest relationship, although highly significant, was between ages 18 and 32. 2 tables and 30 references